Refactor of main and beacon activites, and others

[Sonderful]

This is a fairly large change, but the intention is not to change any behavior for users, rather it aims to refactor the code slightly, from what appears to be mostly auto-converted code.

• Replaced findViewById with synthetics in MainActivity and BeaconActivity where appropriate.
• Made several changes to those classes, and other related classes, to make things a bit more null-safe, a bit tidier, and a bit more idiomatic.
• Reduced visiblity of the Ranging button click handler by registering the click listener in code instead of the layout file.
• Increased visiblity of the TTSManager onInitListener because it was referenced from the unit tests, but not compiling for me.

I'm happy to try to answer questions if there are any. I'm on Mattermost if a longer discussion or explanation is wanted.

[skraynick]

@Sonderful please check the mattermost chat. I believe we were axing the beacon stuff. I will hold off until you respond.... thanks.

[skraynick]

@Sonderful please check the 1 comment... thanks.