v1.350: CW offset config, extension enabling, waterfall & frequency scale panning fixes

From the CHANGE_LOG file:

v1.348,349,350  November 23, 2019
    Admin config tab: add initial CW offset field.
        Kiwi owners/admins: If you don't like the default 500 Hz this is where you change it.
        Non-owner/admin users of a Kiwi have to change the passband manually as usual.
    Admin extension tab: add user enable for each extension.
        Don't want users using a particular extension on your Kiwi? Disable them here.
        Only works for internal extensions currently (i.e. not for the antenna switch extension).
        Local connections (same network) are exempt from these restrictions.
    Fixed specifying frequency in URL when configured in transverter/downconverter mode.
    Fixed premature end of waterfall panning when dragging near left edge.
    Improved behavior when dragging in the frequency scale.