[TITokenField] Added bool .forcePickSearchResult to TITokenFieldView so that user must pick a search result when typing into the field. Like on Facebook message app.
[TITokenField] Fixed bugs with .forcePickSearchResult=YES.
[TITokenField] Fixed issue where addToken: does not get rid of placeholder text.
[TITokenField] Got rid of side effect.

- Separated setSearchResultsVisible: from being called in resultsForSearchString: to reduce side effecting.
[TITokenField] Fixed shadow dissapearing when deleting token during forcePickSearchResult = YES
Merge pull request #50 from remind101/master

Property added to prevent TITokenField from tokenizing unknown recipients.