Update package name in development PKGBUILDs.

Be consistent with magnum-git from AUR.
GLEW wasn't dependency for ES packages.

It's been [0] days since last issue caused by copypasting.
Shaders: `const` for readonly variables is since GLSL 4.20.
Shaders: fix textured Phong for GLSL 1.20 and GLSL ES 1.0.

I desperately need unit tests for shader compilation.