UI: Adjust all indents to 4 spaces instead of 3
* Done using QtCreator's auto-indent functionality on each file
UI: Don't show the big take snapshot button if the currently selected call tree item is not an API call.
* Snapshots can only be taken on API calls
Fixes to get default FB snapshot working on Intel w/ MESA

Use XGetWindowAttributes to get window size in place of glXQueryDrawable.
Mesa glXQueryDrawable has trouble reading width and height.

Use OpenGL calls instead of glX calls for vogl_get_default_framebuffer_attribs.
That will be portable to systems not using glX.

Modify order of linking vogleditor so that X11 comes last.
Condition state capture and restore of state related to ARB_imaging extension.

Some drivers (such as Mesa) do not support GL_ARB_imaging extension. Make the
state capture and restore of state added by this extension be conditional based
on driver support of the extension.
Only save GL_TEXTURE_BUFFER objects when they are supported

Detect if GL_TEXTURE_BUFFER objects are supported by the driver and only save them in the case when they are.  Intel MESA doesn't currently support them so this prevents assertions.