Add support for multiple JQL queries mapped to separate Things projects

[reidab]

This adds support for configuring additional JQL queries, each mapped to separate Things projects

Additional projects are defined by adding THINGS_PROJECT__<name> and JIRA_JQL_QUERY__<name> entries to the config.

For example, to create separate projects for web and API tickets, you can add:

THINGS_PROJECT__API=API Tickets
JIRA_JQL_QUERY__API=assignee = currentUser() AND updated >= -14d AND project = API

THINGS_PROJECT__WEB=Web Tickets
JIRA_JQL_QUERY__WEB=assignee = currentUser() AND updated >= -14d AND project = WEB

Since there's a 1:1 mapping between Jira tickets and Things tasks, tickets can only be assigned to one project at a time. Because of this, these queries should be non-overlapping, both between each other and with the main JIRA_JQL_QUERY.

This can also be used to separate tickets in the active sprint from those in the backlog:

Configure the "main" project/query as the backlog and add a second project/query for the active sprint:

THINGS_PROJECT=Backlog
JIRA_JQL_QUERY=assignee = currentUser() AND updated >= -14d AND (Sprint IS null OR Sprint NOT IN openSprints())

THINGS_PROJECT__ACTIVE=Current Sprint
JIRA_JQL_QUERY__ACTIVE=assignee = currentUser() AND Sprint IN openSprints()