* Create system webhook column (and migration)

* Create system webhook DB methods

Based on the default webhook ones

* Modify router to handle system webhooks and default ones

* Remove old unused admin nav template

* Adjust orgRepoCtx to differentiate system and default webhook URLs

* Assign IsSystemWebhook when creating webhooks

* Correctly use booleans for IsSystemWebhook

* Use system webhooks when preparing webhooks for payload

* Add UI and locale changes

* Use router params to differentiate admin hook pages

* Fix deleting admin webhooks and rename method

* Add clarity to webhook docs

* Revert "Remove old unused admin nav template"

This reverts commit 191a20a738.

* Rename WebHooksNewPost to GiteaHooksNewPost for clarity

* Reintroduce blank line lost during merge conflict

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

Partially implement #770.
Add "Default Webhooks" page in site admin UI.
Persist to the existing webhooks table, but store with RepoID=0 and OrgID=0.
Upon repo creation, copy the set of default webhooks into the new repo.