Ability to mask macros in the frontend

Sometimes, Macros are used to store sensitive information like passwords or shared keys. (think VMWare, Telnet, SNMP).

When viewing the macros that are configured on a host these are put on screen without any masking. This would allow someone looking over your shoulder to easily spot these secrets. This is even more of a risk in 3.0 where we will be seeing all inherited macros as well.

To prevent this scenario, I would like to be able to specify if a macro should be masked in the frontend, perhaps via a checkbox. To see the macro value one should click on a 'unveil' button or icon.