Moved file format checks to the files handling the respective formats
Added libwebp 0.4.1 to 3rdparty directory

Original repo: https://chromium.googlesource.com/webm/libwebp
Added support for WebP image format
added android cpufeatures library to thirdparty
fixed webp cmakelists to link against cpu features on android
fixed webp cmakelists to compile neon files with neon flag on armv7a (prevents crash at build time)
Added sample program to test WebP file format
Merge pull request #1001 from DanielSWolf/webp

Support for WebP image format