Make history-log available through cache API

[gonzochic]

Subsequent feature to #161 .

Today, if you request a project from the cache you will always get the project including its history-log. The project data itself will always take up the same amount of space but the history-log will grow with every change on the project. This means it will be potentially a lot larger then the rest of the project data.

Since the history-log is in most cases not needed it we should think about removing it from the ressource(s) API of the cache and make it available through a separate API (e.g. getProjectLog())

[mathiashoeld]

Follow up to #252

[galethil]

Closing due to inactivity @gonzochic check if you agree.