Default units for displaying less common quantities

[splatch]

I found that I18nProvider does not have mapping for several standard measures which can be found:

• volume [si: m3]
• flow rate [si m3/h]

There are other situations where lack of these mappings might show up. This is namely all channel types which are defined with %unit% state description format. While they will accept updates and display properly ie. m3 these will lack relevant data in item description.