eet: Adding EET_DATA_DESCRIPTOR_ADD_MAPPING_BASIC to add a basic type to a union.

eet: Adding EET_DATA_DESCRIPTOR_ADD_MAPPING_BASIC to add a basic type to a union.

I added EET_DATA_DESCRIPTOR_ADD_MAPPING_BASIC because I need basic types in unions, and EET_DATA_DESCRIPTOR_ADD_MAPPING is only for structs.
I also modified the example with a float and a string.

Reviewers: cedric

Reviewed By: cedric

Differential Revision: https://phab.enlightenment.org/D313

Signed-off-by: Cedric Bail <cedric.bail@samsung.com>