Netkan warning for archived repos, set bugtracker for GitHub

[HebaruSan]

Motivation

A GitHub repo can be "archived", meaning that it's effectively read-only and very unlikely to ever be updated. Currently some of the netkans that we crawl every 2 hours are probably archived, so it's not necessary to keep checking them, but we don't know about it.

There's a resources.bugtracker property in the spec, but it's only populated manually. Many mods are hosted on GitHub repos where issues can be submitted, but we don't check that.

Changes

• Now if a GitHub repo is archived, Netkan will print a warning suggesting that we freeze that netkan, which will be visible on the status page
• Now if a GitHub repo has issues enabled (not all of them do), resources.bugtracker will automatically be set to that repo's issues list
• The duration of caching of strings from Request fewer GitHub releases and cache string URLs in Netkan #2950 is extended from 2 to 15 minutes, since that's about what a typical bot pass takes
• The warning about ModuleManager syntax now prints the affected filenames to ease investigation
• The ModuleManager syntax regexp is updated to detect post-clauses without leading special operator characters:

  PART:NEEDS[NEBULA]
  {
  

  SCALETYPE:NEEDS[TweakScale]
  {
  

  MATERIAL:NEEDS[RealChute]
  {
  

  PART:NEEDS[Launchpad]
  {
  

[DasSkelett]

I don't know of an archived repository to check the archive detection feature, but I guess we'll find out if it works :P