Implement dynamic validation on QA Pages

Closes gitlab-qa#280

See merge request gitlab-org/gitlab-ce!25704

This provides the user with some context as to why certain ActiveRecord
methods are blacklisted.

Elements now have the ability to be required on pages or not
Currently using the default wait mechanism
Altered the ElementWithPattern Cop to fit new splat for init

This adds Ruby 2.6 support.

The `#reload` makes to load all objects into memory,
and the main purpose of `#reload` is to drop the association cache.

The `#reset` seems to solve exactly that case.

The InjectEnterpriseEditionModule cop would not detect certain nested EE
constants such as `EE::Foo::Bar::Baz`. This could result in it not
enforcing `prepend` being placed on the last line. This commit fixes
this by just performing a string match on the line, instead of relying
on AST matching.

This Cop enforces the rule that injecting EE modules (using prepend,
include, or extend) is done by placing the injection on the last line of
a file, instead of somewhere in the middle. By placing these lines at
the very end, merge conflicts will not happen.