softened version check and set default version to 13.0

[th3hamm0r]

This change removes the check against VALID_API_VERSIONS, which always required changes to the library (eg #496, #502), when a new Graph API version has been released. Instead only the pattern check is executed.

I've also changed the default API version to the latest Graph API version v13.0.

[mssalnikov]

Could this be merged and published on pip?

[DBlek]

Can this be released? or should everyone just fork this package when we want to work with GraphAPI after February?

[b1sar]

@martey could you please review and possibly merge this pr and publish it? Without enabling versions up to v17 this library becomes very very limited for future use.