espeak: provide string length with 0 character, fixes problems with qgc reading out strange values/chars at the end of the sentence

All it does is clutter the terminal and it's not doing anything anyways.

Speech synthesis support can now be disabled (DEFINES+=DISABLE_SPEECH)
Speech synthesis dependencies are now checked before enabling.
When support cannot be enabled, the user is now notified.

Conflicts:
	QGCExternalLibs.pri
	src/GAudioOutput.cc

While testing the previous commit on Windows I found that I could not
compile windows due to include of atlbase.h. This file is no longer
available in SDKs. It is only available in for money versions of VIsual
Studio. Luckily this include was not needed. So I just removed it and
Windows now builds again with just VS Express. Tested all changes on
OSX, Linux and Windows (including speech on windows, which still works).

Fixed Audio output on Linux, works now with systems flite version. Introduced two new alarm/notify sounds