Type verification

[wzorgdrager]

Related issue(s): #160

Description of changes

Added pipeline verification system.

Check-list

Please make sure to review and check all of these items:

• Are the updated classes tested?
• Are the updated classes documented & properly formatted?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

[wzorgdrager]

• Write some integration tests (using pipelinebuilder instead of directly building a graph)
• Think of more corner cases
• Add more complex tests (with StageN objects).

Edge cases:

• Do we care about input/transform stages which are not linked to any transform/output stage ? I.e. stages that write to buffer which is not read.
• Do we care about completely isolated stages?

I would suggest adding warnings for those cases.

[wzorgdrager]

Enable graph verification by default!