For some time now, GitHub is showing cards when we hover over an issue
number which gives us a quick summary of the issue. The issue title is
shown in the card among other things.
Given that and the fact that we already require the issue number to be
specified in the pull request description, it's now moot to
ask the contributors to include the issue title in the pull request
description. So, let's remove this unnecessary burden from them.
* Update ISSUE_TEMPLATE.md
with wiki link and minor formatting changes
* Update PULL_REQUEST_TEMPLATE.md
making the formatting more similar to the issue template, simplifying some language and improving links