WIP Use label not pattern as primary navigation key

[andrewgryan]

Pattern is not as fundamental an attribute as label, for example MDDA and CMIP6 intake drivers do not even use a file system. Also, SQL database locators, while there is a GLOB statement, the results might not relate to the existing file system

[andrewgryan]

@LaurenceBeard this PR is working towards separating Dataset UI from Dimension UI so that I can swap pattern to label as the primary key to select datasets. It is needed by #217 as I've hit a road block trying to support sql_pattern and not pattern for database locators

[andrewgryan]

#222 makes this easier by replacing state with selectors, a View can then specify a label in the construction of a Selector(state, label) and the selector.initial_time etc. will be relevant to that View or whatever algorithm the state suggests to use to find the relevant value.

[github-actions]

Message to comment on stale PRs. If none provided, will not mark PRs stale