WelcomePage: fixes QTC_ASSERT

We have to wait for the QtVersionManager until all Qt versions
are loaded.

Change-Id: Ia6f823660d0252fb8e8ee1b8cfaec32e26ebc0bd
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
WelcomePage: adding icons

Adding icons for Blog, Community, Help and Sessions.
Also removing unused old icons.

Change-Id: I8f2c31ad233b852aed137e280505d26708bc9d28
Reviewed-by: Eike Ziller <eike.ziller@digia.com>