Add PIN code to lock IO

[raoulh]

A nice feature to have could be to be able to lock a specific IO with a PIN code. It allows for example to lock a input or output and a specific keyboard would be displayed when trying to modify the variable. It could be used in alarms or to lock critical parts of the configuration (heating control that can only be changed by parents and not childrens...)

Implementation details:

• add a parameter to an IO, locked="true"
• when this is found you need to send the PIN code with the action command to actually execute it.
• the PIN code is stored in local_config.xml
• maybe having different PIN code to create "groups". It allows to have different kind of access rights. lock_group="parents", lock_group="children"
• In the GUIs we need to implement a dialpad to enter the code easily.
• the dialpad can also be used to unlock the screen when it's suspended