Release 1.12.4

Notable changes:
 2019-09-20 84e46ecc Leandro Stanger chore(packaging: flatpack): Add tag release (#254)
 2019-09-15 f02b8e5a actionless fix(oomox_gui: settings): don't fail if config file is not a correct json (ref: #262)
 2019-09-15 4899896d actionless chore(plugins: theme: arc): update submodule (tag: 20190910 + 11 commits)
 2019-09-14 d7e05230 actionless chore(plugins: theme: materia): update submobule (tag: v20190912)
 2019-09-03 a9ed1ec2 Vlada Makhonina Add Baloon theme
 2019-08-11 63515376 Gideon Wolfe chore({scripted_,}-colors: xresources): first attempt at universal reverse theme (#258)
 2019-08-06 8937dc20 actionless chore(plugins: icons: papirus): update submodule (tag: 20190802+ 35 commits)
 2019-08-05 640618b4 actionless chore(plugins: oomoxify): update submodule (replace new red color on disliked Radar/Discover song)
 2019-07-30 f8146b51 actionless chore(packaging: flatpak): sync with git@github.com:flathub/com.github.themix_project.Oomox.git