Adding libwebp: Adding clean copy of libwebp 0.4.0

This commit imports libwebp 0.4.0, including AUTHORS, COPYING, ChangeLog,
NEWS, PATENTS, README and src directories. In src, only includes header
and source files.

The patches required to build it in Qt will follow in separate
commit(s).

Task-number: QTBUG-14205
Change-Id: I747918fe2a07716f66cffb795129f7aa5e067759
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Adding libwebp: Patches to libwebp 0.4.0 for Qt usage

Task-number: QTBUG-14205
Change-Id: Id7c3f4d9398b613a18033d8f3f624448f31ce33d
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Added webp image format plugin

Also added auto test and config test.

This plugin was disabled on winrt and android.

[ChangeLog] Added webp image format plugin.

Task-number: QTBUG-14205

Done-with: Liang Qi <liang.qi@digia.com>
Change-Id: I9409e894d7fc1aef9dce4ffdff8bdf483d689774
Reviewed-by: Ivan Komissarov <ABBAPOH@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>