Use long press instead of tap to display clipboard menu

User research findings

During the usability tests of Tor VPN 0.6.2 (tpo/ux/research#69 (closed)), 2/6 participants had trouble pasting a bridge line from email into the text area. They tried a "long press" gesture to make the clipboard menu appear and be able to paste, but Tor VPN displays this menu on a single "tap" gesture instead.