Fix locale during package upgrade

When installing a package, concrete5 forces en_US. Let's do the same
also when upgrading an already installed package.
Localization for Url Slugs

Various change for locationation of url slugs
Keywords: remove duplicates, standardize format
Synchronize install and update keywords for 5.6.0
Add page keywords for new 5.6.1 page
Merge pull request #1082 from mkly/condensed_urlify_commits

Localization for Url Slugs
Merge pull request #1087 from mlocati/intelligentsearch-i18n-v2

Dashboard keywords alignment for install & update
Merge pull request #940 from mlocati/fix-locale-during-package-upgrade

Fix locale during package upgrade