Make channel-based download url to fix Bug 987330

Also remove major_version context variable in favor
of model method
Merge pull request #1822 from jgmize/relnotes-download-url

Make channel-based download url to fix Bug 987330
Bug 943398: Add Sentry error reporting.

Disable admin email mailing. This was being done
in funfactory in the logging config. The new logging
config included in this commit overrides that.
Merge pull request #1781 from pmclanahan/add-sentry-error-reporting-943398

Bug 943398: Add Sentry error reporting.
Map v23 release notes to bedrock to fix bug 988746

Release channel only; firefox desktop and for android