Add configuration system for core renderdoc module

* This allows persistent config storage and registering tweak variables that
  works independent of the UI's configuration.
* Config vars can be debug only, which means they will be compiled out in stable
  version releases. This allows for debug-logging tweaks that are available in
  all builds (including nightly builds) for diagnostic purposes, but have zero
  overhead in stable releases.
* Variables have a loose hierarchy defined with _ or . to separate nodes.

qrenderdoc/Code/pyrenderdoc/qrenderdoc_stub.cpp

@@ -107,6 +107,10 @@ bool PersistantConfig::SetStyle()
   return false;
 }
 
+PersistantConfig::PersistantConfig()
+{
+}
+
 PersistantConfig::~PersistantConfig()
 {
 }
@@ -159,15 +163,6 @@ void RemoveRecentFile(rdcarray<rdcstr> &recentList, const rdcstr &file)
 {
 }
 
-void PersistantConfig::SetConfigSetting(const rdcstr &name, const rdcstr &value)
-{
-}
-
-rdcstr PersistantConfig::GetConfigSetting(const rdcstr &name)
-{
-  return "";
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // RemoteHost.cpp stubs
 ////////////////////////////////////////////////////////////////////////////////