Improve themes

...ku/quasseldroid_ng/ui/settings/data/AppearanceSettings.kt

app/src/main/res/layout-sw720dp-land/activity_main.xml

app/src/main/res/layout-sw720dp/activity_settings.xml

app/src/main/res/values/strings_preferences.xml

app/src/main/res/values/styles_widgets.xml

app/src/main/res/values/themes_base.xml

app/src/main/res/values/themes_gruvbox.xml

app/src/main/res/values/themes_solarized.xml