[#81142624][WIP] Start of UI for uploading images
First commit. [ci skip]
Rename serializer
Make mixin for select2 assignees.
Add admin page.
Remove possible admins and editors from tasks.
Switch over reviewers to select2.
Fix adhoc toolbar button animations
Merge with master
Subclass Select2Component. [ci skip]
Merge branch 'master' into select2ify
update standard task gemspec
Separate out initialization callback.
Duplicating AttachmentUploader for now :(

For some reason when AdhocAttachmentUploader inherits from AttachmentUploader Sidkiq decides to
ignore AdhocAttachmentUploader and invokes AttachmentUploader directly.
Merge remote-tracking branch 'origin/master' into images_in_adhoc_card
Paper editor spec works.

For some reason solr doesn't seem to be indexing against first or
last name in test, only username and email.
Add rubocop
Fix integration spec for reviewers
Show all admins/editors without searching.

Clean solr before each test.
[#81142624][WIP] Image upload progress and preview