Better matching for @mention

Problem Definition

The @mention feature uses a "contains" match for the REST query to find suggested users. The JavaScript part of the feature uses a "starts with" match.

In some environments this means no users will be suggested even though there are users that could be shown. This makes it hard to use the @mention feature.

Example:

• User types "@joh".
• REST API returns 10 records: mention-rest-joh.txt
• Very few records are shown b/c this customer uses "LastName,FirstName" and random account IDs.

Suggested Solution

• Make the JavaScript use a "contains" search just like the REST call.
• Split on "," in addition to space characters to find the parts of the Display Name.

mention-search-contains.patch.txt

(This patch could not be tested because I had trouble running JIRA from source. It's offered to help identify the relevant code)