deprecate global methods for min/mag filters etc

* deprecates global methods for min/mag filters, and texture wrap as per discussion in #2191 since these methods assume a texture to be bound at point of call - which could lead to undefined behaviour.
rename maxFilter -> magFilter

rename to be consistent with OpenGL nomenclature
add member variables tracking min/mag, wrapmode

* this allows ofTexture to keep track of min/mag filters and wrapmode
clarify docs re: ofEnableArbTex

* We should deprecate / rename of[Enable|Disable]ArbTex method: after all, "ARB" is very generic, meaning "architecture review board", referring to the author of the extension rather the content / name of the extension itself.

I would suggest renaming this method: ```ofEnableRectTex``` or ```ofEnableTexRectangle```.
focus docs re: compression

+ mipmaps are independent of compression, the docs for ofTexCompression suggested otherwise.

+ also adds note about textures having to have multiple-of-four dimensions for most hardware compression options.
rename texData.tex_coords

+ renames texture coordinates to be in line with GLSL convention. width == s, height == t
cleanup ofTexture::loadData()

+ removes outdated comment (situation in comment only affects pot textures, link dead)

+ removes compressed mipmaps based on deprecated glu methods
remove compression query from loadData()

+ clean up loadData a little further
+ texture compression easier implemented afresh
remove mipmap/compression comment

removes a possibly misleading comment about mipmaps & compression
implements mipmaps for ofTexture

+ add generateMipmaps() method to ofTexture

This method:
* checks for compatibility with the current texture target based on GL/GLES compilation target
* uses hardware-accelerated method glGenerateMipmaps()
* checks for availability of method based on GL extension, GL version
adds ofTexture::setMipmapAuto()

+ allows mipmaps to be generated automatically when textures are loaded, and works as a flag indicating wheter a texture wants mipmaps.
add error checking to setTextureMinMagFilter

+ checks whether min/mag settings are valid for current ofTexture context
+ logs one-time warning if error detected
Revert "rename texData.tex_coords"

This reverts commit 2182760b6c82cd1536c4a20660f23bb22d20211b.
update setCompression doxy

adds warning: not yet implemented
implement [dis|en]ableMipmap() syntax

+ follows @ofTheo's suggestion in making the mipmap syntax more straightforward:

+ call mTex.enableMipmap() before you load a texture to auto-generate mipmaps and automatically set the min-filtering for this texture to the OpenGL default, GL_LINEAR_MIPMAP_LINEAR.

 + doxy now notes side-effect minFilter state change.

+ polish syntax to use singular for mipmap, since one mipmap is generated per texture, also follows OpenGL API
uses bind() / unbind() in favour of direct GL

+ this is an extra-precaution to make sure setTextureMinMagFilter does not alter the current texture target bind state should it be called with an already bound texture.
update changelog

Introduces changes to ofTexture in CHANGELOG
add additional GLES check for generateMipmap

+ checks availiability of glGenerateMipmap, based on OpenGL (core since version 3) or OpenGLES (core since version 2)
+ removes ofGetOpenGLVersionMajor() from GLES code path through #ifdef.
Merge pull request #3146 from tgfrerer/feature-ofTextureMipmaps

Feature of texture mipmaps - ready for review