Migrate code to use async/await features along with down level compile by typescript.

[gautamsi]

• use async/await in all calls to server

remaining:
arguments.length does not work when using async function in es5 code.

[PhilHannent]

Hi, I was excited to see you'd made good progress with this. I was wondering if you wanted help with testing. Our setup uses the calendar extensively and I can create a test run of a branch. I'm not sure what is still to do but if it was close then I'm happy to run through some tests and report back.

[gautamsi]

I am going to make some improvement soon and create a test build