Custom template improvements

[AntonPetrov]

This PR includes several improvements that address challenges pointed out by R2DT users in the industry:

• Streamline creating private templates and using them locally in a fully automated way
• Document creating new templates using RNAcanvas and XRNA-React
• Use the --quiet command line option throughout the code to reduce the amount of console output
• Fix a problem where Infernal mapping failed and posterior probability visualisation failed if large insertions were removed (this generated lots of errors and warnings in tests).

As a side product of these changes, running tests produces much less output and it is easier to spot errors:

r2dt.py test 
.......................
----------------------------------------------------------------------
Ran 23 tests in 240.719s

OK

[github-actions]

Docker image tag(s) pushed:

rnacentral/r2dt:pr-129

Labels added to images:

org.opencontainers.image.created=2023-12-07T13:22:26.230Z
org.opencontainers.image.description=Visualise RNA secondary structure in consistent, reproducible and recognisable layouts
org.opencontainers.image.licenses=Apache-2.0
org.opencontainers.image.revision=6f65f5c5b864ac30d0f1b0e377ea78f8adddbae3
org.opencontainers.image.source=https://github.com/RNAcentral/R2DT
org.opencontainers.image.title=R2DT
org.opencontainers.image.url=https://github.com/RNAcentral/R2DT
org.opencontainers.image.version=pr-129