Warnings: missing initializer for value_tables and function type cast (GObject)

Warnings: missing initializer for value_tables and function type cast (GObject)

I fixed the warnings:
warning: missing initializer for field ‘value_table’ of ‘GTypeInfo’
warning: cast between incompatible function types
by replacing the handwritten type info code with G_DEFINE_TYPE...
macros (preferred). When this was not possible due to usage of
base init functions I added casts and the initializer.