docs: Fix typo

(cherry picked from commit 12f9860e2dd43fc726d10717ba4c900af90600f2)
fixes docs typo: AngularJS
(cherry picked from commit 225092add5d7b1a2bf3f3fcf688023a4adead632)
docs: Add Mopidy-Musicbox-Webclient to the web extensions list

(cherry picked from commit eedaf0eb3b10a5bf02350a2608cc599f82475bfe)
docs: More concistent format for web extensions

(cherry picked from commit 249dcf92c46d5a7d215c87b834475b84b7881550)
docs: Add install instructions for the web extensions

(cherry picked from commit da18a599ac5a9c03931def4f6167e4000e0b3c0b)
docs: Add Mopidy-HTTP-Kuechenradio

(cherry picked from commit 0e2866df307a8a1aa54879afea1ab3725fa7eacd)
docs: Kuechenradio doesn't have a screenshot yet

(cherry picked from commit 580e5b079fb31b1ba6df6bfd5235272939e2dfc2)
docs: Put screenshot between description and install instructions

(cherry picked from commit 52baf639929fd5b94169c5fb179330f900d2fd7e)
docs: Remove duplicate extensions

(cherry picked from commit 456faee9483e9b8407d0fd4c8dd472c4ae4e20cd)
docs: Update Mopidy-HTTP docs wrt the HTTP server-side API

(cherry picked from commit 713bca384a4eebd63b2d0fbe4eabf7ffb2ad4191)
docs: typo in Mopidy-HTTP
(cherry picked from commit 839108e7c56aaacebac349835448e40027abef91)
readme: s/Mailing/Announcement/

(cherry picked from commit b2c1b9d4db91d72552a2f3f82f730898d4da07e9)
docs: Update Debian docs with 'mopidyctl'

(cherry picked from commit 933cbe1dce9d596116bb20aa51ab9008fe70d0b3)
docs: Make extensiondev example and API docs for validate_environment() match

(cherry picked from commit 31c874b3eb57ac5e26ae0f72455d12c54ba7625e)
docs: Replace /etc/mopidy/extensions.d with /usr/share/mopidy/conf.d

(cherry picked from commit a1aad39c137ab92afc17332a3b91e3f60488ea17)
docs: Fix typo

(cherry picked from commit c7a6a2abd9a941da6accf9ffa0d03094c9fd9f6b)
models: Hide empty lists from repr()

(cherry picked from commit 305a76486d59a4fd24f335b16c80854dd0a232df)

Conflicts:
	docs/changelog.rst
models: Fix equality for fields set to the default

Fixes #837

(cherry picked from commit bdd1fb983b3abbbb604686e63647a8aaaa5d97a0)
Merge branch 'release/v0.19.x' into develop

Conflicts:
	docs/changelog.rst
	tests/test_models.py