Display open issue count for JIRA filter

[guusdk]

When a project uses a JIRA filter to track issues that are up for grabs, the website should list the number of open issues (as it does for other trackers).

JIRA provides a REST API that can be used to collect the data. This can be used by supplying the filter identifier.

Given an up-for-grabs URL like this: https://igniterealtime.atlassian.net/issues/?filter=10004, take the filter ID (10004 in this example), and use it in a REST API call on the same site, like this: https://igniterealtime.atlassian.net/rest/api/2/search?jql=filter=10004

This will return a JSON result. One of the first few attributes returned is a 'total' count, that can be used on the up-for-grabs website:

{
   "expand":"schema,names",
   "startAt":0,
   "maxResults":50,
   "total":14,
   "issues": [