core: add support for set keyboard indicators PDU

Server Set Keyboard Indicators PDU MS-RDPBCGR 2.2.8.2.1

* add server side code
* add support for client callback
xfreerdp: add support for PlaySound

Using X keyboard bell.
xfreerdp: add support to set keyboard indicators

* add generic function to check for X extensions
* detect x keyboard support
* add callbacks and client code to set/clear keyboard indicators
Merge pull request #2136 from bmiklautz/feat/kbd_indicators

Support for set keyboard indicators PDU