Fix issues identified in the expert review done by jaster on our installation instructions

Originally created by @anonym on #14548 (Redmine)

See notes/mac_install.mdwn in the Summit 2017 Git repo.

Open issues

• #15130: Restructure our support pages
• #15120 (closed): Improve style of command lines

Will be solved by other projects in 2021

• #15103 (closed): The note about Tor bridges in Greeter should be closer to the actual option
• #15109 (closed): Rename 'Persistence wizard' as 'Persistence assistant'
• #15118 (closed): Mention in persistence assistant to only enable the features that are needed
• #15128 (closed): Link to Mac known issues from troubleshooting

Subtasks

• #15111 (closed): Improve style of buttons
• #7495 (closed)
• #8897 (closed)
• #14788 (closed)
• #15099 (closed)
• #15100 (closed)
• #15101 (closed)
• #15104 (closed)
• #15105 (closed)
• #15106 (closed)
• #15108 (closed)
• #15110 (closed)
• #15112 (closed)
• #15113 (closed)
• #15114 (closed)
• #15117 (closed)
• #15119 (closed)
• #15121 (closed)
• #15122 (closed)
• #15123 (closed)
• #15124 (closed)
• #15125 (closed)
• #15126 (closed)
• #15127 (closed)
• #15129 (closed)
• #15137 (closed)