Bump version to v0.42.0

Notable changes:

Verified contacts
  - Ability to verify a contact's safety number, same for group's
    members via the 'Show members' screen
  - Check mark next to verified contacts, and next to
    100%-verified groups
  - Synchronization of verification decisions across devices
  - Banner and confirmation on send when previously-verified safety
    number changes
  - Confirmation on send if safety number has changed very recently
  - Updated message detail screen when a message fails due to a safety
    number change

Delete individual message from message detail screen

Clearer error text when a message to a group partially fails

Icons for in-conversation timer change and key change notifications
We now drop duplicate messages when we receive them

A number of reliability fixes:
  - New 'unprocessed' cache for messages not yet fully processed,
    attempted re-process on startup
  - Protections against 'wedged' conversations, which won't receive or
    send messages until restart
  - Better resilience to errors throughout the codebase

Application loading screen until server backlog is fully processed
  - Shows messages processed so far
  - Prevents large numbers of notifications from firing on application
    startup

Conversation loading screen

Unloading of conversations and old messages due to inactivity to reduce
memory usage

Potential fix for "Too many message keys for chain" (caused after
desktop is offline for long time)

FREEBIE

Author: scottnonnenberg

manifest.json

@@ -4,7 +4,7 @@
     "name": "Signal Private Messenger",
     "short_name": "Signal",
     "description": "__MSG_installTagline__",
-    "version": "0.41.3",
+    "version": "0.42.0",
     "offline_enabled": false,
     "minimum_chrome_version": "37",
     "default_locale": "en",