Add optional dependency installation

[katarinasupe]

Add the possibility to choose which dependencies to install and which not, when installing GQLAlchemy.

For example, pip install gqlalchemy installs all dependencies, and we define extra dependencies that don't have to be installed necessarily for basic GQLAlchemy usage. For example, docker, networkx and neo4j would be extra dependencies. If you want to install them, you would run something like:

pip install gqlachemy [all]

or for just one extra dependency:

pip install gqlalchemy [docker]

and for more than one extra dependency:

pip install gqlalchemy [docker, networkx]