Support optional permissions

• add new options to request optional permissions like downloads
  • with downloads, closeDownloadBar will be able to keep your tab groups unchanged
  • if the flag #extensions-on-chrome-urls is enabled, now work on the native New Tab Page on Chrome 85+
    • note: only tested on Chrome, and other browsers like MS Edge may refuses this injection
  • contentSettings has been moved to optional, so in a fresh installation toggleCS may not work but show an error tip
• fix a compatibility issue about fullscreen on new MS Edge
• VisualMode: fix behavior of w on Firefox
• LinkHints: support exclude: css-selector to exclude special elements
• add vimium://sed, sed-p and sed2
  • see 41e2396 for detailed usages
• Firefox: allow restoring an incognito tab if incognito="force"
• Chrome: moveTab now keeps tab in its group, unless group="ignore"
• add some other options to commands like zoomIn, toggleMuteTab
• fix some bugs