feat [close #105]: Add property to decide wether to add includes per stage

[axtloss]

Adds a new property addincludes which lets the user decide if a stage should include the includes.container

closes #105

[taukakao]

Just curious, why was this approach chosen instead of just checking if the path exists?

[axtloss]

This is per stage, a user may want to include it during the testing stage but not the building stage, just checking if the directory exists wouldn't help

[taukakao]

I see, interesting. But yeah, makes sense to me.