Alpha version of label indexes.

Squashed messages from 9 commits:

9.
Properties now uses PropertyFamily and contained classes.
Fetching,seting,clearing properties can be done with PropertyFamilyKey or PropertyTypeKey.
Hierarchy of newly added clases is:
Vertices -n-> PropertyFamily {name: String} <-1-n-> PropertyType {type: Property::Flags}
Edges -n-> PropertyFamily {name: String} <-1-n-> PropertyType {type: Property::Flags}

PropertyFamilyKey -> PropertyType
PropertyTypeKey -> PropertyType

PropertyType t0,t1;
let t0!=t1 be true
let t0.family==t1.family be true

then next is true
PropertyTypeKey{&t0}!=PropertyTypeKey{&t1}
PropertyFamilyKey{&t0}==PropertyFamilyKey{&t1}
PropertyFamilyKey{&t0}==PropertyTypeKey{&t1}
PropertyTypeKey{&t0}==PropertyFamilyKey{&t1}

8.
Intermedate commit.
Noticed that integration queries throw SEGFAULT.

7.
Defined interface for indexes.
Fixed three memory leaks.
Fixed integration_queries test which now passes.

6.
Commit which return Xorshift128plus to valid shape.

5.
Tmp commit.

4.
Label Index is compiling.

3.
tmp

2.
Vertex::Accessor now updates Label index.

1.
Applied changes for code review.

src/database/db.cpp

@@ -1,4 +1,5 @@
 #include "database/db.hpp"
+#include "storage/model/properties/property_family.hpp"
 
 Db::Db() = default;
 Db::Db(const std::string &name) : name_(name) {}