Fix the spelling of "optimize"
Clarify the usage of 'db_user' and 'omero_database'

...as discussed in devteam on the evening of 22 February.
Make instances of 'db_user' and 'omero_database' bold
Fix a typo
Fix the default values warning so that it is actually built
Merge pull request #263 from melissalinkert/upgrade-page-fixes

Upgrade page fixes