meson buildtype - use plain not debug as debug will be insanely slow

eina cow backtraces on write make this impractically slow to use
debug. also the switch back to dev mode was not the reverse of
switching to release mode. this fixes that.

meson.build

@@ -1,6 +1,6 @@
 project('efl', ['c','cpp'],
   version: '1.22.99',
-  default_options : ['cpp_std=c++11'],
+  default_options : ['buildtype=plain', 'cpp_std=c++11'],
   meson_version : '>=0.47'
 )