Better support for overloading start and destroy methods in Session

Move functionality from static start and destroy functions into instance
methods, allowing these to be overloaded. This works the same way as
calling Session::set() which then in turn calls inst_set()

Additionally use Injector to create the default Session instance to
allow the class to be swapped out.
Update javascript.md

Replaced deprecated jQuery live() with on(), updated link to documentation.
Merge pull request #3228 from daslicht/patch-1

Update javascript.md
Merge pull request #3216 from halkyon/session_inst

Better support for overloading start and destroy methods in Session
Adding some more commonly used SS_Log priority constants.
Merge pull request #3225 from halkyon/log_constants

Adding some more commonly used SS_Log priority constants.
Update i18n.php

Correct common_languages for Norwegian to use 'nb' and not 'no'
Merge pull request #3230 from tscole/patch-1

Update i18n.php