No option to disable all GUI transitions/animations

**Describe the bug**

Currently there is no option in Droid-ify to disable all GUI transitions (animations). System-wide settings are said to be unsuitable for this (#31). It's unfortunate that transitions cannot be completely disabled due to accessibility reasons (#228 for example) and since Droid-ify otherwise runs very well on slower/outdated devices.

There are also two related feature requests opened in the issue tracker. The first is to change the tab-switching animation (#102) and the second is to have a switchable app page-loading one (#247). This report extends #247 to all transitions and completely solves it if transitions were individually switchable. While #102 certainly is a feature request and #247 is somewhere in between, a global animation switch is more of a basic functionality.