Improve CONTRIBUTING

Noting that we don't take feature requests or 'help me' stuff on the Issues tracker should cut down a ton on bad Issues.

This reverts commit 5d95f320.

log 404 status when ActiveRecord::RecordNotFound was raised (#7646)

Rename .rb template handler to .ruby to avoid conflicts with mustache classes

Allowing pass couple extension to one register_template_handler call

Fix collection= on hm:t join models when unsaved

If assigning to a has_many :through collection against an unsaved
object using the collection=[<array_of_items>] syntax, the join models
were not properly created, previously.

Add missing entry in CHANGELOG about change of AD::Session::MemCacheStore

Remove unncessary code.