ENH: Update SimpleSpinEditor to allow floats and be able to specify the step of the spin control.

Currently the SimpleSpinEditor is only applicable to integer values and the step/increment of the spin control is fixed to the value of one (click on spinner, arrow up/down or rolling the mousewheel) or 10 (PageUp/PageDown).

For greater flexibility it would be great if the SimpleSpinEditor could also handle float values and that the step used in the spin control could be specified explicitly.

It would also be great if the SimpleSpinEditor would behave similar to the wx.FloatSpin, which by the use of modifier keys
`Shift`, `Ctrl`, `Alt` will increase the step value for the spinner by a factor of 2, 10 and 100, respectively.
A combination of `Shift`, `Ctrl`, `Alt` increment the step value by the product of their factors.
`PgUp` & `PgDn` = 10 * increment * the product of the `Shift`, `Ctrl`, `Alt` factors;