Merge pull request #22 from thiagomt/master

I'm merging this now and I'll do my fixes on the top of your changes. Thanks again, you are great!
Fixing issues found by WebStorm
Merge branch 'master' of github.com:kdzwinel/Context
Improving code responsible for checking status of contexts.
Code formatting and small improvements.
Fixing bug on options page - context after cloning wasn't fully functioning.
Also, code formatting.
Preserving state of 'highlight ungrouped extensions' checkbox between options page reloads.
Removing social icons on options page when user is offline.
Using Chrome Sync to store context configuration.
Adding missing strings to translation files. Updating polish translation. Updating cleanup.php script to PHP 5.3+.
Fixed cleanup.php script and new messages added to all messages.json files.
Merge branch 'messages_fix' and update polish translation.

Conflicts:
	_locales/cleanup.php
	_locales/de/messages.json
	_locales/en/messages.json
	_locales/es/messages.json
	_locales/fr/messages.json
	_locales/it/messages.json
	_locales/ja/messages.json
	_locales/pl/messages.json
	_locales/pt_BR/messages.json
	_locales/zh_CN/messages.json
Updating polish translation + small improvement in cleanup.php.
Changing 'show first extension icon' option from radio button to checkbox.
Updating translation files.
Updating extension version and release notes.
Code formatting, strict mode, spelling and other small fixes.
Adding documentation.
Removing 'add new context' option from notification window as it doesn't work on OSX (can't enter text to the input field).
Removing 'ask what to do' option for browsers that do not support HTML notifications - #23.
Update README.md

Using github markdown shortcuts in README.md (hopefully these will work).