New type:value locator syntax in addition to (or instead of) type=value syntax

[pekkaklarck]

WhiteLibrary seems to support syntax like type=value with its locators similarly as SeleniumLibrary. The syntax is problematic, though, because it clashes with Robot's named only argument syntax as issue #48 demonstrates. The syntax was also considered problematic with SeleniumLibrary, and it has supported type:value syntax since SL 3.0. For more details see robotframework/SeleniumLibrary#908.

In my opinion it would be good for WhiteLibrary to support the type:value syntax as well. Because the library is still pretty young, I'd actually recommend deprecating the old syntax in the future to have only one syntax in the end.