Conversion function naming

[rgrieder]

If you look at src/util/Convert.h you can see in the public section almost at the end of the file, that we have tons of different functions that do the same.

That is not such a big problem, most of the are very useful indeed. But the issues are:

• There is "convertValue" and "ConverValue", that's a bad idea
• I have chosen "omni_cast" to speed up writing short conversions. The name is quite bad and someone made a suggestion for a new name: "multi_cast". Is that more appropriate?
• Furthermore, getConvertedValue and omni_cast do the same. We could easily merge them. The difference is the order of the template parameters.

[rgrieder]

Deleted the upper case versions and renamed omni_cast to multi_cast. Having both multi_cast and getConvertedValue shouldn't be a problem, esp. because getConvertedValue supports a fallback value.