Update CHANGELOG

- Add HTML5 notifications
- Add Screwdriver theme (not included yet… but soon!)
Fix import/export view

Some bugs introduce because I was tired surely ;)
Fix problem token

Token was present in RSS url even without token value.
Option to hide (or not) feeds/categories with no unread article

https://github.com/marienfressinaud/FreshRSS/issues/430
https://github.com/marienfressinaud/FreshRSS/issues/575
Reading config: change order of settings

https://github.com/marienfressinaud/FreshRSS/issues/430
SQLite: Bug creation new users

Not tested much yet. Some MySQL parts changed a bit too to double-check.
https://github.com/marienfressinaud/FreshRSS/issues/574
Merge branch 'dev' into 411-update-system
Add basic system of update

- Check on update.freshrss.org for new updates
- Download script
- Apply script
- Need translations and verifications

NOTE: current script on server indicates version 0.7.3 is an update
of 0.8-dev ==> IT'S ONLY FOR MY TESTS!

Script just does a backup of ./data actually...

See https://github.com/marienfressinaud/FreshRSS/issues/411