Experimental WebKit GWT renderer on Linux

[Alexander.Mitin]

Under Linux there is a quite big knowledge base of various issues related to Mozilla/Xulrunner, so we decided to switch the GWT renderer to use the WebKit engine.

This requires GTK+-2.20 (and later) and WebKitGtk+-1.2 (and later) to be installed, and works for both 32-bit and 64-bit systems.

To enable WebKit support, grab the latest GWT Designer build and set the "__wbp.linux.useWebKit" system property to "true" (e.g., add "-D__wbp.linux.useWebKit=true" to your Eclipse starting command line).

In the future, we will use WebKit as the mainstream renderer in GWT Designer. It is also planned for for WebKit to become the default GWT renderer on Linux.