Draft: multiple accounts

[alangecker]

first draft of multiple element instances in the same electron BrowserWindow.

Works so far, but there is still a lot to do (see ToDo list) and I can't promise that I'll find time for that in the next weeks 🙃

related element-hq/element-web#2320

ToDo's

• proper react menu with (webpack?) building
• show badge counts in menu
• aggregate badge counts for tray
• open correct instance on notification click
• make multiple profiles optional (via lab flag?)
• apply a change in theme to all instances + menu
• menu i18n
• menu styling
• instance chooser for protocol links
• bring back electrons dropdown menu
• accessibility
• how to handle 'page-favicon-updated' and 'page-title-updated' now? (tray.ts)
• tests
• proper session partition naming, renaming possible?
• migration of existing sessions

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[yuuyins]

nice! i think the UI should be iterated. instead of using yet another column for that which convolutes the UI, try using the already existing user button in the top left for switching accounts.

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