[Graphics] Redirect GetAddress(string)

GetAddress(string) now calls GetAddress(IntPtr) internally. This
reduces the number of APIs that must be implemented for each platform.
[Graphics] GetAddress(string) is no longer needed
[Mac] Sped up extension loading

From ~200ms down to ~65ms on a rMBP with Nvidia 650M and Mac OS X
10.9.2.
[Bind] Do not generate DllImports

These break dynamic loading of OpenGL ES and bloat OpenTK.dll with
duplicated strings. The new extension loading mechanism is now fast
enough to make DllImports unnecessary.
[GL][ES] Do not break public API

Even if that API is not meant to be used by applications.
[GL][ES] Regenerated bindings