Create application-collabora-webjar

[ChiuchiuSorin]

Is your feature request related to a problem? Please describe or add steps to reproduce your use case.
Make the JavaScript code easier to reuse.

Describe the solution you'd like
Create a WebJar to allow easier reuse of some JavaScript functions.

[oanalavinia]

Can you update this issue description to make it more general? As mentioned in #73 (review) , right now you mention your use case (i.e. add collabora buttons outside this code), but that's just one purpose. So you should actually say this issue is for refactoring JS code and as a result it's easier to reuse it in other use cases like xwikisas/xwiki-pro-macros#549