Add reloadActiveSession

[leonvogt]

This PR will add the function reloadActiveSession to the TurboNavigator, to reload the currently active session (modal or main) without the need of performing a new visit or navigation.

If you wanted to reload the active session before this change, you first had to find out whether the modal or main session was active.
In addition, you had to pass in the sessions during initialization in order to reload it if desired.

This changes would come in handy, if you wanna reload the active session, after the app comes back to foreground or for handling internet connection loss.

[joemasilotti]

@leonvogt, is this different than #150? I feel like they both solve a similar problem. But maybe both are needed.

[leonvogt]

@joemasilotti, your PR #150 looks promising. They indeed solve a similar problem.
I'm unsure at the moment if our solution is really needed if your PR is merged.

If its ok for you, I'll wait for your PR to be merged and try to accomplish the same tasks with your solution.
If everything works fine, I'll close this PR.

[joemasilotti]

Closed in favor of #184 and #183.