Offer alternative MessageFormat renderer to resolve CSP issues

[oliversalzburg]

Due to the way MessageFormat is implemented in angular-translate, it is not possible to build a satisfactory CSP (#1227). The MessageFormat.js team suggests to pre-compile your expressions and not use the compiler at runtime. The current implementation in angular-translate specifically relies on the runtime compiler though.

The MessageFormat.js team suggested that there is an alternative implementation in intl-messageformat (messageformat/messageformat#180) that could be utilized, which doesn't have the same CSP implications.

I'm currently testing https://github.com/fairmanager/angular-translate-interpolation-intlmessageformat and it seems to work fine just as a drop-in replacement. I think it would be nice if an alternative renderer could be offered officially with this package or if the topic could be addressed in documentation.