[CaBundleUpdater] Correct the error handling when downloading bundle
[AdBlockSubscription] Fix infinite loading of subscription when cannot write to file
[Mac] There is no /proc filesystem on Mac

Closes #1294

[ci skip]
[QzCommon] Move constants initialization into source file (.cpp)

Plugins are now checking for a match of version that were built with
in Plugin::testPlugin() function.
1.6.5 is now current stable release

[ci skip]
[Styles] Don't mention to use [style=QtStyle] selectors in comment

It is not available in current Qt releases

QzSchemeHandler+AboutDialog: Fixed coding style
[ToolButton] Cleanup code + removed unused properties
[ToolButton] Manually handle showing menu

ToolButtons now don't have menu indicators.
This fixes issue with Back/Forward buttons in Navigation Toolbar
being more wide than other buttons.
[ToolButton] New function to set look of button as it was in toolbar

Currently, it only sets the correct icon size
[Themes] No longer needed to set menu-indicator to none for ToolButtons
[ReloadStopButton] It is now only one button

Instead of hiding and showing two buttons (reload and stop), use
only one ToolButton and change the object name accordingly.
[Build] Fixes building with Qt5
[TabWidget] Don't save qupzilla:restore page in closed tabs
[ComboTabBar] Fixed tabAt() on scroll buttons
[ToolButton] Don't try to show menu when it is already visible
[ToolButton] Added property "toolbar-look"

This property makes it possible for themes to customize look of
additional ToolButtons in Navigation Toolbar.
[ChromeTheme] Make use of a new ToolButton "toolbar-look" property
[LocationBar] Make sure text format is correct even when text doesn't change

refreshTextFormat() is using page's url to determine which part of
displayed text is host. Url of page may not change immediately when
starting loading.
This commit makes sure that text format is correct with every
WebView::urlChanged() signal.
[LocationBar] Fixed showin progress over text. Use opacity with QPainter

Not the best solution, but probably the easiest.
Closes #1261
[Themes] Fix loading linux.css and mac.css on Mac/Linux