Refactor:
- TextureData to handle Pixmap and Custom TextureType
- TextureData consumeCompressedData to consumeCustomData
- GLTexture function to uploadImageData to custom mipmap level

Added:
-MipMapTextureData which handles multiple TextureData to be uploaded to single mipmpa levels
MipMapTextureData fixes
Changes updated
Fix up some tests
Added default styles

Many people use the default skin for testing scene2d.ui, because it is the only one available AFAIK.

Calling any of the following will result in an exception, because the default skins which are set in the constructors do not exist in the uiskin.json:

`ProgressBar progressBar = new ProgressBar(0, 100, 1, true, skin);`
`ProgressBar progressBar = new ProgressBar(0, 100, 1, false, skin);`
`Slider slider = new Slider(0, 100, 1, true, skin);`

Thus I added some styles for those cases.
Added support for Net.openURI
Merge pull request #1689 from nooone/patch-1

Added default styles
Merge pull request #1690 from davebaol/openuri

LiveWallpaper and Daydream: added support for Net.openURI
Merge pull request #1688 from alex55i/tests-patch

Fix up some tests
Merge pull request #1664 from lordjone/texturedata

TextureData refactoring and mipmaps