Spout graphs command can now take filter flags, closes #31.

- The following flags are available:
  - `spout g --type-numeric`
  - `spout g --type-integer`
  - `spout g --type-choices`
  - `spout g --size-lg`
  - `spout g --size-sm`
  - `spout g --type-numeric --size-sm`
- For specific variables the following can be used:
  - `spout g --id-<variable_id>`