WIP: trying to define graph schema
WIP: creating titan keys/labels from a generic schema
Added FinalVertexType which contains a set of properties (with automatic evidence of SmthHasProperty)
WIP: Experimenting with sets of properties
Returned popertyTypes set back
Returning some schema-related stuff back, but the test still doesn't work (no Case1 implicit)
Added dependencies to schema definition; added default values; changed version to distinguish snapshots
* Added a feature to filter out properties that are associated with a particular vertex-/edge-type;
* Added to schema values with sets of pairs (vertex/edge-type, it's properties);
* Added `has` method to vertex/edge types to associate several properties (a type-set) at once;
* Simplified `HasProperty` (removed `SmthHasProperty`, etc.);
* Renamed `HasProperties` trait (about getters) to `CanHaveProperties`;
* Removed right-associative property getter (`ReadFrom`);
* Renamed `AnyProperty.PropertyOf` to `Property.Of`;
Fixed creation of titan-schema from an abstract one (+tests);
review code, minor renamings and modifications
Renamed PropertyTypes to just Properties
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Merge branch 'feature/schema' of github.com:ohnosequences/scarph into feature/schema
Merge branch 'feature/schema' of https://github.com/ohnosequences/scarph into feature/schema

Conflicts:
	src/main/scala/ohnosequences/scarph/Schema.scala
General refactoring
Merge branch 'feature/schema' of https://github.com/ohnosequences/scarph into feature/schema
generate docs, move ops out of the type, rename schema
Renamed Schema file to GraphSchema