linux: Writes crash report upload log
linux: Put crash dumps under "/tmp/ProductName Crashes/"
linux: Put "uploads.log" under "/tmp/ProductName Crashes/"
win: Writes uploads.log
Add crashRepoter.getLastCrashReport API
docs: crashRepoter.getLastCrashReport
Merge pull request #810 from atom/report-back-crash-id

WIP: Add API to get last crash report ID