chore(release): Remove usage of pushd and popd

Reasons:
1. Not all environments have these (e.g. codio.com).
2. Ending at the root directory of the new branch seems more correct
   than bouncing back to a potentially unrelated directory.
chore(gitignore): Ignore startup.sh, which has special meaning to codio.com
chore(release): install and update node deps before each release
chore(release): continue even if release branch is already created

With git branch/git checkout the script would fail if you had run
it once already and the release branch had already been created.
This makes it so it ignores the fact that the release branch has
been created and just continues on its merry way, which is a more
intuitive behavior than forcing you to clean up the environment
if the script fails the first time.
chore(docs): make tx install command code instead of italics
chore(release): check for dependencies before starting release
chore(mailmap): canonicalize all evan@elgg.org to Evan Winslow
chore(docs): update contact info in readme and contributors
chore(release): separate commit for translation updates
chore(i18n): update translations
chore(release): v1.9.0-rc.2
Merge pull request #6916 from ewinslow/release-1.9.0-rc.2

Release 1.9.0 rc.2