Fix Bug 981909 - copy change related to Firefox Marketplace

Needs l10n updates.
Fix Bug 965823 - Add a custom Twitter timeline widget to the Student Ambassadors landing page
Merge pull request #1858 from craigcook/master

Fix bug 991887 - update MoCo Steering Committee
Update .image-replaced LESS mixin. Bug 977696.
Merge pull request #1851 from kyoshino/bug-981909-marketplace-copy

Fix Bug 981909 - copy change related to Firefox Marketplace
Use rna for fxos 1.3 relnotes to fix bug 988290

Update rna submodule to tweak tag sorting for fxos
Merge pull request #1860 from jgmize/rna-fxos-1.3-relnotes

Use rna for fxos 1.3 relnotes to fix bug 988290
Fix Bug 992564 - Removing address from Contact page
Merge pull request #1861 from kyoshino/bug-992564-contact-press

Fix Bug 992564 - Removing address from Contact page
Merge pull request #1859 from jpetto/bug-977696-fxos-devices-ui-close-button

Update .image-replaced LESS mixin. Bug 977696.
Merge pull request #1642 from kyoshino/bug-965823-ambassadors-twitter

Fix Bug 965823 - Add a custom Twitter timeline widget to the Student Ambassadors landing page
Bug 993297 - Sync page links to an anchor in the sumo article that can't be localized
Merge pull request #1864 from pascalchevrel/bug-993297-Sync_page_fix_anchor_link

Bug 993297 - Sync page links to an anchor in the sumo article