Gulp angular bootstrap

Regarding JS: as we do not have a concatenated js in the node_module, we just use a glob syntax to include all the files:
`./node_modules/angular-bootstrap/src/*/*.js`
Note: only one * for folders, not two (**) or it would also include the tests and it would break our bundle.
The glob syntax is ok in that case as we do not need to require() angular-bootstrap anywhere in our code, so it will only be processed for vendor bundelization.

Regarding fonts: I haven't find a way to put the fonts in specific folders in ./build, so all the fonts (bootstrap + fontawesome) are directly in ./fonts, but I do not think it is too bad.

Regarding SASS/CSS: we cannot have a vendor css bundle because we want to be able to use our vendor SASS variables (and mixins, etc.) in our own SASS code, so we need to compile them all together. It implies vendors SASS sources will be watched. But we probably do not have too many external SASS lib anyway (Bootstrap + FontAwesome should be enough).