proc: refactoring: merge target into proc

- moved target.Interface into proc as proc.Process
- rename proc.IThread to proc.Thread
- replaced interfaces DisassembleInfo, Continuable and
  EvalScopeConvertible with Process.
- removed superfluous Gdbserver prefix from types in the gdbserial
  backend.
- removed superfluous Core prefix from types in the core backend.

service/api/conversions.go

@@ -47,7 +47,7 @@ func ConvertBreakpoint(bp *proc.Breakpoint) *Breakpoint {
 
 // ConvertThread converts a proc.Thread into an
 // api thread.
-func ConvertThread(th proc.IThread) *Thread {
+func ConvertThread(th proc.Thread) *Thread {
 	var (
 		function *Function
 		file     string