291: bug 1402037 - improve shutdownhang signatures (#4017)

* bug 1402037 - improve shutdownhang signatures

We have a number of shutdownhang signatures where the stack is rife with
"uninteresting" bits such that the signature gets truncated before getting to
something interesting or relevant or actionable.

This adds a bunch of things to the irrelevant list such that they don't show up
in the signature.

I did some regression testing and these strings only show up in shutdownhang
crashes. If that changes, we should rethink them on a string-by-string basis.

* Collapse two lines into one

290: Update signature generation documentation (#4014)

We had a wiki page that sort of walked through the process for requesting
signature generation changes. We changed that wiki page to point to these docs,
but didn't have a process in these docs. This adds that.

This also cleans up the process for reviewing changes to signature generation.

289

bug 1390530 - Add https scheme to crash-stats CSP srcs (#4009)

288

Add rtc::FatalMessage -- webrtc.org's implementation for RTC_CHECK/RT…

287

fixes bug 1400085 - add stdext::hash_map<T>::.* to prefix list (#3992)

286

Add rust oom signature (#3977)

285

Bug 1396928 - Add gfxPlatform::Init and gfxPlatform::GetPlatform to t…

284

fixes bug 1395163 - right link to supersearch fields missing in admin…

283

fixes bug 1391402 - $ needs to be escaped in prefix list (#3933)

282: Update and clean up some getting started docs (#3916)

* Update and clean up some getting started docs

I made some changes based on Jonathan's suggestions. The big issue was that the
documentation about running "make dockerupdatedata" was after the link sending
you off to the webapp documentation, so he missed it. This fixes that flow and
adds some more details which are probably helpful to know.

* Improve Quickstart by adding more context explanation

* Clean up tools install section of Getting Started

* Add warnings about outdatedness