Add install and upgrade information for CentOS/RHEL and Ubuntu
Merge pull request #2166 from opf/hotfix/update_docs_supported_distros

Add install and upgrade information for CentOS/RHEL and Ubuntu
Make the installation prerequisites more consistent with regard to CentOS/RHEL, Fedora and Ubuntu
formatting of bullets
rewriting i18n tests as specs
one class variable less
Merge pull request #2165 from opf/hotfix/i18n_testing_as_specs
Fix the URL for the stable branch of Fedora 20 packager
Merge pull request #2172 from lindenthal/release/4.0

Fix the URL for the stable branch of Fedora 20 packager
Fix config_files paths in Hound config
Correct API experimental's users path
Merge pull request #2177 from opf/hotfix/17173_user_related_wp_filters_are_inactive

17173 User related WP filters are inactive
Treat zero as not null
editable description support
Merge pull request #2106 from 0xF013/feature/16988-editable-description
Consider width limitation in wiki
Merge pull request #2179 from opf/fix/17244_wp_attributes_with_zero_value_are_not_shown_in_split_view

17244 WP attributes with zero value are not shown in split view
Make inplace editor buttons accessible
Adapt tests to accessible inplace editor buttons
Merge pull request #2186 from opf/fix/17258_edit_subject_not_accessible_with_chromevox

17258 Inplace editor buttons not accessible with ChromeVox