added group caching feature

[bountyC0d3r]

No description provided.

[ThomasKranitsas]

When caching a group from getGroup we take into consideration the includeSubGroups/includeParentGroups filters. But, the next time we query for the same group ID, we return whatever is in the cache without checking those.

Example scenario:

• Request for group A without parent or sub groups
• The group is fetched from DB and cached
• Request for the same groups again from cache and also request sub groups
• The group is returned without sub groups as it's cached without sub groups

[ThomasKranitsas]

@bountyC0d3r here's the ideal implementation IMHO:

Check cache, if data is in there, check if `sub` and/or `parent` groups are required, if required and not in cache, fetch from DB and update cache. Return data.

This way, we don't fetch unnecessary data for caching but we don't worry about data not being in cache as we're checking before we return it

[bountyC0d3r]

@ThomasKranitsas incorporated the review comments, please check and approve if all is good