Remove TensorBase dependencies from Parser

[oicirtap]

Additions:

• Parser uses TensorVar objects instead of TensorBase objects for creating IndexExpr and Assignment objects.
• New conversion functions between vector and vector<Dimension> for the Type class.
• New TensorBase constructor with TensorVar as single input.
• New assemble and compute TensorBase functions which take in pre-packed arguments.

[fredrikbk]

Needs to be merged in or reimplemented along the same lines. Currently our command-line tool and online code generator allocates memory for tensors, with dimensions 42.