Provide a development guide to move atlasboard forward

[JonathanL]

In light of the dragging issue I filed and other issues I've noticed, it would be nice to make changes to the atlasboard code.

• Server-side development is simpler, editing the ./cli directory, but a walkthrough would be a good idea.
• Client-side is more opaque. I tried to muddle through it while looking at the dragging problem and installed bower and gulp and maybe did it - in an attempt to update to a more recent gridster. But I'm still not sure what to edit, for example, to add the gridster dragging workaround. E.g. ./assets/build/app.js is clearly not the right place.

(Other potential feature ideas: show last update time (from a UI and backend job point of view), add the fullscreen mentioned elsewhere, etc).

[JonathanL]

I note that there is this which has SOME of the information: https://bitbucket.org/atlassian/atlasboard#markdown-header-atlasboard-core-development