feat($parseProvider): add the additionalIdentChars configuration method

[gurdiga]

Allows extending of the set of character allowed in identifiers used in Angular expressions.

Updated the property name and also renamed the branch. #4747

[petebacondarwin]

Let's get this into 1.5

[lgalfaso]

@petebacondarwin to do this right we would need to:

1. split the checks into identifier start and identifier continue
2. take care of some browsers quirks
3. handle chars that in UTF16 need more than 1 chars

At a minimum we would need 1 and 2

[mercibe]

Really needed feature. Please do not forget it in 1.5! Tired of manually patching each new Angular version...
Thank you very much in advance!

[lgalfaso]

Now that bd0915c and ad29894 landed, this can be closed