chore(demo): re-structurize demos

A proposal for a demos structure.
* demo files are moved to the demo directory
* js files moved to the demo/js directory
* localization files moved to the demo/l10n directory
* fixed Grunt.js and .gitignore according to the new structure

A list of demos is not complete. There are some new demos and
some rewritten old demos.
Merge pull request #51 from DWand/chore-demo

re-structurize demos
feat(translateProvider): add methods to use different missingTranslationHandlers

This commit adds  useMissingTranslationHandler and  useMissingTranslationHandlerLog (as a shortcut for the former).

It also introduces a new factory service  which could then be used in application using  useMissingTranslateHandlerLog().

It is now possible to add any kind of missing translation handler and tell angular-translate to use it.

BREAKING CHANGES:  missingTranslationHandler is no longer supported since its functionality will be replaced with  useMissingTranslationHandlerLog.
Merge branch 'missing-translation-handler' into canary
Merge branch 'canary'
Update package files and changelog