Merge v0.8 into master

#### NB Upgrade notes
Please ensure you read and follow `docs/upgrade_specifics/upgrading_v0.7_to_v0.8.md` after following the usual upgrade guide!

Fixes:
- Fix errors caused by assets loaded via HTTP on HTTPS served instances (thanks @LunarchildEU)
- Fix versioning for the `pheal-ng` dependency (thanks @ppetermann)
- Fix a few cases that would result in Starbase names being unresolvable.
- API jobs will no longer be submitted a second time if an existing one is already working/queued (thanks @gregoryduckworth)
- General skill search fixes (thanks @gregoryduckworth)
- Fix the manual update job submission for Corporation API Keys (thanks @gregoryduckworth)
- Fix a case where characters with multiple API keys were not correctly added to people groups
- General documentation updates and fixes (thanks @Nutbolt52)

New:
- A pretty 'Registration is disabled' page has been added (thanks @gregoryduckworth)
- Added a corporation roles view with a roles change log (thanks @LunarchildEU)
- The recently released PI API Endpoints have been added is will update with characters that allow access to their assets lists. A frontend will be made available in a next release.
- API Related errors can now be deleted on mass
- Character Market Orders are now exposed via the frontend
- Corporation Market Orders are now exposed via the frontend
- Almost all tables are now sortable and filterable
- Assets views now include the the volume for items, containers and the whole station combined (thanks @gregoryduckworth)
- It is now possible to delete *all* the historical information for a character/corporation API Key when deleting a key.
- The character view will now show other characters if the character is part of a person group.
- A optional skill level can now be specified when searching character skills
- Introduced a help page and SeAT update checker