Block out pages needed for ux_guide

Add resources stub to ux_guide home

Fill out principles and basics

Add TOC to basics

Move all of UI guide to new UX guide structure

Add first level structure on ux-guide pages

Add more details to buttons

Add button images. Update link on development

Renamed surfaces to templates. Add tooltip details

Update typography and icons on Basics page

Add images for color. First draft of voice and tone

Delete findings page

Refine pages. Fill out Surfaces pages

Clean up layout on basics, surfaces, features. Add anchorlinks and counts to components

Fill out components page

Add item title and system info block

Fill out Features page

Switch tooltip placement image

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It was previously possible for invalid credential errors to go unnoticed
in this task. Users would believe everything was configured correctly and
then sign in would fail with 'invalid credentials'. This adds a specific
bind check, plus catches errors connecting to the server. Also, specs :)

https://gitlab.zendesk.com/agent/tickets/48003

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Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17981421

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17981448

[e44da1c] Add Label API expected keys to tests

[ac929c8] Update Label API documentation

Add documentation for the "Only allow merge requests to be merged if all discussions are resolved" feature

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

No matter which environment Gitlab was running as, the admin/logs view
always showed production.log. This commit selects the logfile based
on Rails.env.

- Rename ProductionLogger to EnvironmentLogger
- Make EnvironmentLogger logfile depend on env
- Update spinach test for log tabs

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This was the only thing using the `sdoc` gem, which was blocking another
gem from updating.

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Correct the command to get a gdb backtrace from all threads. `apply` is
not a valid gdb command.

See https://sourceware.org/gdb/onlinedocs/gdb/Threads.html#Threads .

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