Made taxbrain install script more usable

[codekansas]

I had a lot of difficulty hard-resetting my environment (partly being on a slow internet connection) and I figured it would be good to make some changes to the install script. Mainly:

1. Making it more interactive, so that the user can decide what should be run and what shouldn't. To get the previous behavior, use yes | ./install_taxbrain_server.sh
2. Making it so that it always fails if something goes wrong, using set -e option - this avoids a bunch of the || return 1 stuff from the previous script and is probably a more sane way to do things
3. Batched conda / pip installs (this was previously messing with me because of the aforementioned poor internet connection)
4. Added some documentation on what is doing what

I also noticed that there were a lot of redundant source activate aei_dropq && source webapp_env.sh so I added the first part to the webapp_env.sh script, so you only have to do source webapp_env.sh. Maybe there was a reason for keeping them separate? I'm not sure. @hdoupe

[hdoupe]

Thanks for re-working the install_taxbrain_server.sh script. It's much faster now. I've always taken an "ain't broke, don't fix it" approach with this since I didn't fully understand what was going on.

I'm going to to need some time to go over this and make sure everything is still working as expected.

[hdoupe]

Can you still specify which version of these packages that we want to use?

[codekansas]

You could do that after the script runs, or by changing the script. I guess right now it just gets the most recent one available.

[hdoupe]

We need to be able to specify the version in the script. It's pretty common to have to pin to an older version. Each parameter change and API change requires a change on the PolicyBrain side. These tend to happen a lot. And on occasion they break something on the PolicyBrain side that we don't have time to solve at the moment.

[hdoupe]

That was a fun one. See #799

[hdoupe]

This PR looks good. Once you add back the capability to set the taxcalc, btax, and ogusa versions, this should be good to go.

@GoFroggyRun can you take a look at this PR?

[GoFroggyRun]

@codekansas thanks for simplifying the installation script as well as providing those documentation.

I don't have much technical output regarding the script, but was wondering whether it‘d make sense to update README.md (Local Deployment Setup in particular) within this PR?

[codekansas]

@hdoupe I believe it just uses the versions of those that are in the various requirements files. I'd thought there was something important about the install order (which there seemed to be from the previous script) but it doesn't seem to be the case.

@GoFroggyRun It shouldn't change anything, as it just gives the user more options on what they want to do and makes things download faster.

[hdoupe]

@Kpinkelman would you mind taking a look at this script? Here are a few things you can check:

1. If django=1.9 is specified in requirements.txt, will this script install django 1.9?
2. If taxcalc=0.10.2 is specified in conda-requirements.txt, will this script install taxcalc=0.10.2? Repeat for different versions of btax and ogusa.
3. Compare the time required to setup the environment with the current install_taxbrain_server.sh script and this proposed version. (You should be able to do this via time ./install_taxbrain_server.sh --all)

Run these tests with ./install_taxbrain_server.sh --all.