Not showing respondents page in SupportFlow in menu

There's no situation where someone would want to add a respondent term
directly, instead of adding them to the ticket, so the Respondents screen
should be hidden.

Fixes #166
Replaces usage of word respondent by customer

Just a case sensitive replace
Migrate all terms with taxonomy sf_respondent to sf_customer during upgrade
Merge pull request #168 from VarunAgw/minor-change

Change "Respondents" to "Customers"