IMOS checks on "LATITUDE", "LONGITUDE" and "TIME" too specific

[mhidas]

These checks only look for the variables with names LATITUDE, LONGITUDE and TIME (same issue for vertical variables already fixed - aodn/compliance-checker#61). These are not required to have these specific names (though in most IMOS data they do), and should be identified according to their name or attributes. e.g. LATITUDE is any variable that has

• variable name in _possibley list (cf/util.py), OR
• standard_name="latitude", OR
• axis="Y", OR
• units in _possibleyunits list (cf/util.py)