Add custom email headers for repository and result.

This allows more specific filters on the emails based on the
headers and e.g. the build results.

Fixes #1577.
Remove '[travis-ci]' from IRC message

That part is superfluous. Fixes
https://github.com/travis-ci/travis-ci/issues/2363
Deliver as many webhooks as possible.

If one fails, this only raises the error at the end, giving others,
potentially more successful ones, a reason to pass.

Motivation is that other webhook deliveries shouldn't suffer from
one webhook in the chain not being able to deliver.

The downside is a possible duplication in deliveries for the ones
that have succeeded.

Fixes travis-ci/travis-ci#2356.
Refine spec for multiple webhook deliveries.
Mark errored builds as red in HipChat.

The grey used has insufficient signal to recognize a build with an error
among the normal chat noise.

This also improves logging for HipChat messages in case of an error
pushing the message to the API.
Include error message in HipChat logs.
Support multi-line templates for Slack.

The Slack integrations make it very simple to have multiple lines
in a message, so we might as well utilize it.
bundle update

also use the metriks-librato_mertrics gem
update github_status task logging

this brings the format inline with what is used for all other addons
add some fancy bundler args
use actionmailer 3.2.x

if we don’t specify this then 4.x is used, which doesn’t work with travis-support.

plus, if we specify a activesupport version, but not an actionmailer version, then bundler goes crazy and resolves forever

and ever

and ever
tweak the github commit status error message spec
fix some rspec deprecation warnings
a couple more rspec deprecation warnings
backtrace_clean_patterns is now backtrace_exclusion_patterns
update webhook logging
updating soooo many messages

well, only 1 this time
correct the webhook error messages
we love ca$hing
update the readme just a tad