Allows the loading screen code to compile with implicit string
conversions disabled.
While we're at it remove unnecessary const usages, and add it to nearby
variables where appropriate.
In our error console, when loading a game, the strings:
QString::arg: Argument missing: "Loading...", 0
QString::arg: Argument missing: "Launching...", 0
would occasionally pop up when the loading screen was running. This was
due to the strings being assumed to have formatting indicators in them,
however only two out of the four strings actually have them.
This only applies the arguments to the strings that have formatting
specifiers provided, which avoids these warnings from occurring.
With shader caches on the horizon, one requirement is to provide visible
feedback for the progress. The shader cache reportedly takes several
minutes to load for large caches that were invalidated, and as such we
should provide a loading screen with progress.
Adds a loading screen widget that will be shown until the first frame of
the game is swapped. This was chosen in case shader caches are not being
used, several games still take more than a few seconds to launch and
could benefit from a loading screen.
