[webapp] hide toolchains tab if harbour is visible

Harbour is only visible if we have Sailfish customization
 - the SDK already has all the necessary toolchains installed
 - no toolchains can be removed
 - additional toolchains cannot be installed

Also do not require that request url always ends in a slash.

Force provider update when 'check for updates now' is clicked.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>