RFR: 1554: Fold JEPBot into PR bot

[Erik Joelsson]

This patch removes the JEPBot and moves the functionality into the pr bot module, similar to what SKARA-1851 did for CSRBot. Instead of introducing a new JEPBot in the pr bot module, I'm using the existing `IssueBot` from SKARA-1912 to poll for updated JEPs to process PRs for. 

The handling of different kinds of "Issues" in CheckRun was (and still to some extent is) rather messy. I've tried to tidy it up a bit in this patch, but didn't want to take it too far in a single change. In the CheckRun, all issues are fetched in one place and stored in maps which are then used throughout the check run. This also limits the amount of places where failure handling is needed. Hopefully  SKARA-1963 can improve this aspect further. I also didn't want to change too much of the CSR issue handling in this patch, but I see some room for improvement there too.

Now that all JEP issue handling is done in the pr bot module, we don't need to communicate between bots using labels. Despite of this, I chose to leave the `jep` label working the same way as before: Adding it when the jep command is issued for adding a jep requirement and removing it when that requirement has been fulfilled, and also re-adding it if the requirement for some reason is no longer fulfilled. I think this will be the least confusing to users. However, one could also imagine the `jep` label just staying around signaling that this was a JEP PR, even after a PR has been integrated.

The JEP test in `CheckTests` has been enhanced to verify that updates to the JEP issue are detected and handled, and that the label is updated accordingly by `CheckRun`.

The issue metadata hash has been extended to include issue state and resolution, so that CheckRun will re-evaluate if any of those fields change for a JEP issue. Since we now have a separate `IssueTrackerIssue` interface, I chose to expose these fields directly through two new accessor methods instead of having to deal with complex and untyped properties everywhere. I've also added default values for status, priority and type for `TestIssueTrackerIssue` so that it mimics `JiraIssue` better in regards to those fields, and removed the null checks in the metadata hash calculation.

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Commit messages:
 - All defaults in same place
 - SKARA-1554

Changes: https://git.openjdk.org/skara/pull/1535/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1535&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1554
  Stats: 1044 lines in 21 files changed: 185 ins; 716 del; 143 mod
  Patch: https://git.openjdk.org/skara/pull/1535.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1535/head:pull/1535

PR: https://git.openjdk.org/skara/pull/1535