Update to elementary OS 7 runtime

• Fix missing application window title (#222)

• Redesign of the headerbar!
• Update elementary OS runtime to 6.1 (#207)
• Remove unnecessary sandbox hole for accountsservice (#215)
• Fix slow switching of channel views when there is a large number of users (#210)
• Fix auto-scrolling to be more reliable and simpler (#211)

• Use non-symbolic icons in the headerbar (#123)
• Re-open application to the last chat view (#187)
• Use new icons for server items in the side panel (#199)
• Fix parsing of ACTION messages causing empty private messages to appear (#153)
• Fix inability to reconnect to a server if it dies without restarting the application (#203)
• Fix app icon badge not clearing with private message chat view regains focus (#208)

• Updated Dutch translations by Vistaus

• Integrate with OS notifications to display a notification when mentioned in a channel or private message (#23)
• Display the number of unread mentions as an application badge in the dock (#24)
• Set initial default nickname and real name based on system user account (#171)
• Fix marker line in chat views showing incorrectly when font scaling other than 1x is used (#182)
• Fix incorrect handling of network availability state (#189)
• Fix the "restoring connections" overlay not appearing on startup (#190)
• Fix incorrect parsing of command-line arguments (#193)
• Revert the overly-restrictive 8-character nickname limit in the server connection dialog (#197)

• Add ability to browse a curated list of IRC servers (#156)
• Fix parsing of MODE messages which caused crashes when connecting to certain servers (#184)

• Respect the system light/dark style preference (#150)
• Support SASL (plain and external) authentication (#16)
• Fix autoscrolling when receving QUIT messages (#152)
• Fix text not wrapping for errors on server connection (#167)
• Fix window size and position not saving (#170)
• Fix certificate warning dialog not appearing (#172)
• Fix secrets not saving when using the Flatpak installation (#173)
• Fix BrowseChannelsDialog not using Granite.Dialog (#176)
• Fix new auth tokens not saving when editing a connection (#179)

• Fix Stripe public key (#164)

• Fix flatpak runtime version to be stable 6 (#163)