(Navascript) Add a condition tag

[rfrankhuizen]

This is to avoid the usage of message mode="ignore" when you only really want to group a set of statements under a single condition without having to repeat said condition.

Marte agrees this would be a good extension (she is typing this)

Suggested format:

<condition expression="Some expression to be evaluated">
</condition>

[billgemist]

@rfrankhuizen Maybe the name will be like this? In order not to have too many "condition" <block condition="Some expression to be evaluated"> </block>

[rfrankhuizen]

Yes, even better!

[rfrankhuizen]

Added