Show referenced MRs & Issues only when the current viewer can access them
This addresses both issues identified in #6066.
## The private MR by user `remy2` with a note referencing to a public issue

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** before the fix

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## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** with the fix

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## The public issue viewed by user `remy2` with the fix (no change)

See merge request !2405
- Removes redundant "Create a broadcast message" scenario that was
entirely covered by the "Create a customized broadcast message"
scenario.
- Adds "Edit an existing broadcast message" scenario
- Adds "Remove an existing broadcast message" scenario
Dropdowns for clone. Star and Fork with new count areas. Star and Unstarred Works now
Fixes#2876 and #3482
Used existing styles. <br/>
Did not attempt to make pixel perfect as styles already exist. <br/>

See merge request !2156
Automatically fork a project when not allowed to edit a file.
Fixes#3215.
To do:
- [ ] Add tests
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## "Edit" button on file in a project the user does NOT have write access to

## Clicking will automatically create a fork

## When the fork has been created, the user is returned to the edit page on the original project with a notice

## The user cannot change the target branch and is informed that editing will start an MR

## Hitting "Commit changes" will commit and start an MR from my fork to the origin project

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## "Create file, "Upload file" and "New directory" buttons in a project the user does NOT have write access to

## Clicking any of these options will automatically create a fork

## When the fork has been created, the user is returned to the tree page on the original project with a notice

## Clicking "New directory" again will show the modal. The user cannot change the target branch and is informed that editing will start an MR

## Hitting "Create directory" will commit and start an MR from my fork to the origin project

cc @dzaporozhets @skyruler
See merge request !2145
Add JS validation for invalid characters in branch name
Fixes#3293
Demo:

See merge request !2122