ui_server: add backtrace reporting functions
ui_server: add backtrace reporting functions

The glibc provides a way how to access the backtrace of function
calls. It can be useful for debugging of certain bugs or finding
sources of exceptions.

Example (wrapped, shortened):

build/ui-server(_ZN6BeeeOn16stdout_backtraceEv+0x1f)[0x43048d]
build/ui-server(_ZN6BeeeOn19TRestRequestHandlerINS_15MongooseR
		equestENS_16MongooseResponseEPvE13handleReque
		stERS1_RS2_+0x472)[0x43537c]
build/ui-server(_ZN6BeeeOn15TMongooseServerIPvE6handleEP13mg_c
		onnectionP12http_message+0x1c7)[0x4344d5]

[skipped many lines...]

/usr/lib/libPocoUtil.so.31(_ZN4Poco4Util11Application3runEv+0x1
		f)[0x7f117971712f]
build/ui-server(main+0x5a)[0x42ed48]
/usr/lib/libc.so.6(__libc_start_main+0xf1)[0x7f1178543741]
build/ui-server(_start+0x29)[0x42ec09]

Reviewed-by: Petr Stehlík <34fd672d4ba535a5cc62ffb15c811632a40953f1@stud.fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server