BSpinner: do not redefine fValue

BSpinner had its own fValue defined instead of using the one from
BControl. This results in the be:value in the message sent when the
control is invoked to always be 0.

Change-Id: I1cff5f30adbf5b1dede57a14377cd4e1db7a30d3
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7428
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

BSpinner: Set min value then max value

... reverse this to avoid confusion, you'll see why in next commit.

No functional change intended in this commit, functional change is in the
next commit.

Split BSpinner into BAbstractSpinner and...

2 concrete classes which are currently implemented:
* BSpinner (works on int32s)
* BDecimalSpinner (works on doubles)

In addition BAbstractSpinner now inherits from BControl instead of
BView/BInvoker. This allowed for code simplification at the cost of needing to
cast for the decimal version because SetValue(int32 value) comes from BControl.

Also, add a spinner_button_style enum with 3 options:
* SPINNER_BUTTON_HORIZONTAL_ARROWS
* SPINNER_BUTTON_VERTICAL_ARROWS
* SPINNER_BUTTON_PLUS_MINUS

which sets the spinner arrows to either use horizontal arrows (left/right)
vertical arrows, (up/down), or +/- symbols (the default).

If the spinner button is using horizontal arrows you can decrement and increment
the spinner value by pushing control+left/right, otherwise you can increment and
decrement by pushing up or down. The reason for needing control is so that you
can move the cursor in the textbox otherwise.

Switch the 3 apps that are currently using BSpinners to use the integer variety
in Deskbar preferences, WebPostive preferences, and Screen preferences.

Spinner: Generalize actions into methods

Add an Increment(), Decrement(), and SetValueFromText() method.

These can be overridden by derived classes.

Spinner: Move ValueChanged up

... along with the other hook methods

Add BSpinner class based on GCI2013 work

Split BSpinner into BAbstractSpinner and...

2 concrete classes which are currently implemented:
* BSpinner (works on int32s)
* BDecimalSpinner (works on doubles)

In addition BAbstractSpinner now inherits from BControl instead of
BView/BInvoker. This allowed for code simplification at the cost of needing to
cast for the decimal version because SetValue(int32 value) comes from BControl.

Also, add a spinner_button_style enum with 3 options:
* SPINNER_BUTTON_HORIZONTAL_ARROWS
* SPINNER_BUTTON_VERTICAL_ARROWS
* SPINNER_BUTTON_PLUS_MINUS

which sets the spinner arrows to either use horizontal arrows (left/right)
vertical arrows, (up/down), or +/- symbols (the default).

If the spinner button is using horizontal arrows you can decrement and increment
the spinner value by pushing control+left/right, otherwise you can increment and
decrement by pushing up or down. The reason for needing control is so that you
can move the cursor in the textbox otherwise.

Switch the 3 apps that are currently using BSpinners to use the integer variety
in Deskbar preferences, WebPostive preferences, and Screen preferences.

Spinner: Generalize actions into methods

Add an Increment(), Decrement(), and SetValueFromText() method.

These can be overridden by derived classes.

Spinner: Move ValueChanged up

... along with the other hook methods

Add BSpinner class based on GCI2013 work