KmsHttpLoop: Add internal loop class

Change-Id: Icb2ac521e9f300175f15e1db83cc368e92b5c5fd
KmsHttpEPServer: Integrate main loop

Change-Id: I51317bf3fd8f2e1a3ae4e1e0be11599c7623dd52
KmsHttpEPServer: Use proper macros for returning from g_source callbacks

Change-Id: I11ae883feb85317987962858c446efa8be8b1119