Implement query handler

[ekampf]

Implement a base handler that can handle GraphQL queries and mutations. Inspired by https://github.com/graphql-python/graphql-django-view

• [x] Base GoogleAppengine webapp2 handler that answers GraphQL queries

Example - sample app (cookbook?) to also use in the http://graphene-python.org/ docs - move to separate branch

[coveralls]

Coverage decreased (-2.9%) to 90.837% when pulling ec93a6d1e694cc7a35daac9cb7811188ffb8c128 on feature/base_graphql_handler into 51291ee5e4362c7f3483d4c2035ecabd7e18188c on master.

[coveralls]

Coverage decreased (-3.02%) to 92.095% when pulling 4b0dcbd737fd7891b9a3752f5e003516c67a18d0 on feature/base_graphql_handler into 972a5936a03c5311628f1f57d6c464b92fbfb077 on master.

[coveralls]

Coverage increased (+0.4%) to 95.47% when pulling 5fc1794c3c36b4695bac4785e583ff777e25734f on feature/base_graphql_handler into 972a5936a03c5311628f1f57d6c464b92fbfb077 on master.

[coveralls]

Coverage increased (+0.7%) to 95.848% when pulling e49def026aa8e000a2f648f11fad2b59fb8f7235 on feature/base_graphql_handler into 972a5936a03c5311628f1f57d6c464b92fbfb077 on master.

[coveralls]

Coverage increased (+1.08%) to 96.194% when pulling 120ed279a45ad6bb2c71a5961ad0c42c3f1fe978 on feature/base_graphql_handler into 972a5936a03c5311628f1f57d6c464b92fbfb077 on master.

[coveralls]

Coverage increased (+1.1%) to 96.207% when pulling 95c17bb115504df187867189b7dea9e4a20f260a on feature/base_graphql_handler into 972a5936a03c5311628f1f57d6c464b92fbfb077 on master.

[coveralls]

Coverage increased (+1.1%) to 96.207% when pulling ccee02c538e448dc8ea5f90aefa97a6580c1c171 on feature/base_graphql_handler into c3cff390472ca245ee8addf3751dedf04ced6f10 on master.