f97c4df (after 4.4.3) with accessibility patches

This release includes everything from https://github.com/thelounge/thelounge/commits/f97c4df2 in the upstream repository (which itself includes 2 of my accessibility fixes), plus patches based on the following branches:

• Improve contrast in built-in themes to pass WCAG AA
• Add meaningful headings for easier navigation
• Replace ARIA tabs with router links, improve network sidebar interactivity, and resolve related tooltipped instances
• Resolve other tooltipped instances
  • Note this branch is sequenced after the previous one; I have also submitted a PR using an alternate isolated version of this branch since it is arguably the less complex of the two
• Announce sidebar toggled states
• Add proper focus management to mentions popover
• Allow removing unnecessary connect fields, and allow nick to be empty
• Allow setting hint text for connect form fields (as opposed to pre-filled values) (sequenced after the previous branch)
• Allow customizing client-side message retention limits on active/inactive channels

New configuration options in this version:

• hints
• hiddenNetworkFields
• inactiveMessageLimit