2.0-RC3

This is a bugfix release fixing release blockers for 2.0.

Changes

* Fixes a long-standing security bug that caused unencrypted connection 
  when fetching feed content from Reedah and TheOldReader. Please upgrade
  and change your Reedah / TheOldReader password afterwards!
  (Lars Windolf)

* Fixes #1529: small memory leak in parser initialization
  (Lars Windolf)

* Fixes #1528: TinyTinyRSS not working anymore due to Content-Encoding
  header not indicating JSON
  (Lars Windolf)

* Fixes #1524: mark all read dialog broken
  (Lars Windolf)

* Fixes #1523: replace outdated feedburner URL in default feed list OPML
  (Lars Windolf)

* Dialogs converted to libadwaita: rename, reedah_source, google_source
  (Lars Windolf)

* Drop old migration code for 1.4-1.8 versions
  (Lars Windolf)

* Improved enclosure handling: when using images a large one matching the window
  width will be used (previously sometimes the smallest one was selected due to
  not checking sizes)
  (Lars Windolf)