QmlJSInspector: Enable plugin by default

We disabled it because it should be considered experimental ...
but this creates problems with the debugger setup (Observer pane
doesn't show up even if the plugin is activated).

Carsten Owerfeldt agreed with this.

src/plugins/qmljsinspector/QmlJSInspector.pluginspec

-<plugin name="QmlJSInspector" version="2.0.93" compatVersion="2.0.93" experimental="true">
+<plugin name="QmlJSInspector" version="2.0.92" compatVersion="2.0.93">
     <vendor>Nokia Corporation</vendor>
     <copyright>(C) 2010 Nokia Corporation</copyright>
     <license>