Merge v0.9.1 into master

## NB Upgrade notes

Please ensure you read and follow docs/upgrade_specifics/upgrading_v0.9_to_v0.9.1.md after following the usual upgrade guide!

### Fixes:
- Remove . in mail sending activation links that may break them (thanks @gregoryduckworth)
- Fix a bug relating to the UserTableSeeder that caused new installations to fail

### New:
- Corporation Ledgers Now show nett totals (thanks @gregoryduckworth)
- A user may now login with either a email address or a username (thanks @gregoryduckworth)
- Registered Users now require the "Key Manager" permission to prevent new users from deleting the key a corporation may have asked for for security reasons.

... and a few other smaller UI / backend enhancements and fixes!

#### Release Stats:
*27 commits* in *28 changed files* with * 371 additions* and * 60 deletions.*