Multiple GitGraph improvements: Exclude PR heads, Add branch/PR links, Show only...

Multiple GitGraph improvements: Exclude PR heads, Add branch/PR links, Show only certain branches, (#12766)

* Multiple GitGraph improvements.

Add backend support for excluding PRs, selecting branches and files.

Fix #10327

Signed-off-by: Andrew Thornton <art27@cantab.net>
* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>
* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Only show refs in dropdown we display on the graph

Signed-off-by: Andrew Thornton <art27@cantab.net>
* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>
* use flexbox for ui header

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Move Hide Pull Request button to the dropdown

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Add SHA and user pictures

Signed-off-by: Andrew Thornton <art27@cantab.net>
* fix test

Signed-off-by: Andrew Thornton <art27@cantab.net>
* fix test 2

Signed-off-by: Andrew Thornton <art27@cantab.net>
* fixes

* async

* more tweaks

* use tabs in tmpl

Signed-off-by: Andrew Thornton <art27@cantab.net>
* remove commented thing

Signed-off-by: Andrew Thornton <art27@cantab.net>
* fix linting

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Update web_src/js/features/gitgraph.js

Co-authored-by: silverwind <me@silverwind.io>
* graph tweaks

* more tweaks

* add title

Signed-off-by: Andrew Thornton <art27@cantab.net>
* fix loading indicator z-index and position

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>