Fix for #1343

Changes for BODAAC:
Only store start and end dates if they are valid (which won't happen until the temporal extents are loaded from ncWMS).
Only use dates if they are stored (if no dates are stored then no temporal extent is uded).
Added default dates so that downloads don't break if they're initiated before the temporal extents are loaded.
Don't use dates in updateNcwmsParams if they are invalid.
Ensuring dates are UTC where required
Change way default date is created because of problems in HtmlUnit
Merge pull request #1371 from aodn/Issue_#1343_2

Issue #1343