Raise useful error when waveform_id is incomplete

[calum-chamberlain]

See #563 - some picks from FDSN services are missing channel codes resulting in an opaque and hard to understand error.

What does this PR do?

Adds a useful error message when waveform_ids are incomplete when generating templates.

Why was it initiated? Any relevant Issues?

#563

PR Checklist

• develop base branch selected?
• This PR is not directly related to an existing issue (which has no PR yet).
• All tests still pass.
• Any new features or fixed regressions are be covered via new tests.
• Any new or changed features have are fully documented.
• Significant changes have been added to CHANGES.md.
• First time contributors have added your name to CONTRIBUTORS.md.