Feature of texture mipmaps - ready for review

Following the discussions on #3142, #2191 here's my proposal for programmable + legacy GL ofTexture mipmaps. 

I've tested this on OpenGL 2.1, 3.2, 4.1 on Mac OS X Mavericks, Nvidia GT 750M. 

It would be great to hear whether this works as expected on iOS, RPi and android, if these devices support mipmaps (you should see a one-time warning if not).

To activate texture mipmaps this PR suggests the following syntax:

	ofTexture mTex1;
	mTex1.setMipmapAuto(true); 
	ofDisableArbTex();
	ofLoadImage(mTex1,"grid.png"); 
	mTex1.setTextureMinMagFilter(GL_LINEAR_MIPMAP_LINEAR, GL_NEAREST);
	ofEnableArbTex();

After this, you would draw() the texture using mipmaps.

### Here's a minimal test app as a one-file gist: 
https://gist.github.com/tgfrerer/dae32894b8ef785e6786

### This PR also:
* updates inline documentation where needed
* takes out compressed mipmaps for now (before, mipmaps & compression were bundled together & using a deprecated glu method).
* adds one-time warnings with hints of how to fix common errors, but only in non-performance-critical setup methods.
* gets rid of a bunch of deprecation warnings in OS X
* removes the last hold-out for GLU methods (yay!).

e.g.: here is a case where the behavior of tex_t has changed.