Add google eslint rules as a base

Remove some we don't care about. Set some other ones we do care
about but don't currently adhere to to warn. Set the max warnings
threshold to the current number of warnings, so we don't introduce
more of them. Fix a bunch of legit lint errors and add exceptions
to various places in the test code that does funny things with
'this'.

src/models/event.js

@@ -438,8 +438,6 @@ var _REDACT_KEEP_CONTENT_MAP = {
 };
 
 
-
-
 /**
  * Fires when an event is decrypted
  *