[RFC] NumericUpDown

- [x] The user should not be able to enter invalid characters to the NumericUpDown control.
    An invalid character is defined as character other than:
    - Positive/Negative sign (only if it is the first character)
    - Number
    - Decimal Seperator (only if there is none present)
- [x] Paste action is monitored for illegal input
- [x] Use __Language__ Property instead of __Thread.CurrentThread.CurrentCulture__ for __StringFormat__
- [x] Adjust font size of __+__ and __−__ sign (Fixes #919)
- [x] Allow change of value by pressing __Arrow Up__ and __Arrow Down__
- [x] Add ValidationErrorTemplate to the control
- [x] Allow user to enter Scientific Notation
- [x] Remove inheritance from __RangeBase__ in order to allow following two requirements (???)
- [x] Allow __null__ as valid value
- [x] When value is __null__ then there should be the possibiliity to use a watermark
- [x] Add ClearTextBox
- [x] Implement __SelectAllOnFocus__
- [x] Check if the increment/decrement speeds up by pressing the Up/Down arrow key for a long time

~~Update __Value__ property after each character that is changed by the user (deletion, addition)~~ (Add in a future PR)