Add alpha blending toggle to Aquarium. By default, alpha
blending is disabled. To enable alpha blending, you can
pass "--enable-alpha-blending=[0, 1]" by cmd args.
Replace alpha value of shaders by regex to specify the alpha
value.
Because imgui enabled alpha blending to show text, which renders
text by an gray bitmap, the logic of imgui is revised to show
text when alpha blending is disabled. In addition,imgui is compiled
as source files of the project instead of third party.