Introduce the GET_CONFIG IPC request

This introduces memory usage by one copy of the config file, which is an
acceptable trade-off for being able to easily revert data loss.
The default config is 6KB, user configs will be in the same ballpark.

fixes #2856

src/config.c

@@ -13,6 +13,7 @@
 #include <xkbcommon/xkbcommon.h>
 
 char *current_configpath = NULL;
+char *current_config = NULL;
 Config config;
 struct modes_head modes;
 struct barconfig_head barconfigs = TAILQ_HEAD_INITIALIZER(barconfigs);