Replacing conversion functions to unitconvert

[katarkon]

In last development version all of convert functions (like mhz2mt) were replaced by unitconvert. It makes difficults to switch on new version. It should be better to keep obsolette functions as wrappers to new unitconvert (with corresponding warning).

[Stefan Stoll]

mt2mhz and mhz2mt are available now in version 6.

[katarkon]

Thanks a lot