This size is determined to be the best one with the current set of
device SVGs in libratbag. It is set to ensure that the jump in size
caused by the MousePerspective populating itself when switched to is
minimal and the least disturbing. We can't populate the MousePerspective
in advance because we need to know the device.
The welcome and error screens both require a different "perspective"
into Piper, while being in the same window. For this reason, we
introduce a titlebar and a regular stack and the concept of a
"perspective", which is defined as a certain view into Piper.
A perspective needs to implement an interface of sorts of two methods:
one to retrieve its string name, and another to retrieve its widget titlebar.
Different scenarios can then show different perspectives, that have full
control over the main widget and the titlebar displayed. This commit
introduces the MousePerspective, which is a perspective showing the
mouse configuration. Future commits will add an ErrorPerspective and a
WelcomePerspective, and even further into the future we can add a
KeyboardPerspective as well.
This commits adds the necessary bits in the UI to switch between
popovers. Following commits will propagate profile changes through the
rest of Piper so that all control widgets update corresponding to
profile changes.
