Always compile with -Wall flag.

As a library that is going to have to be used and re-used, it is
important that all potential errors are caught and all compiler
warnings are resolved.
Shut up compiler warnings in TaigaKeybind keystate checkers.

These return statements are never actually reached and exist purely
to suppress the compiler warnings.
Add empty virtual destructor to TaigaConfigSetting

Deleting an object through a pointer to an abstract type actually
causes undefined behavior unless there is a virtual destructor.
Add empty virtual destructor to TaigaActor.

This is done for the same reason as the previous commit.
Add empty virtual destructor for TaigaDrawer

This has been done for the same reason as the previous two commits.
Suppress compiler warnings about signed-unsigned comparisons.

The typecasts here are actually 100% safe, because the values being
converted are guaranteed to be non-negative when being converted
to an unsigned type.