Some fixes and improvements in TALCustomScrollBox

[viniciusfbb]

• Improving the compatibility with TCustomScrollBox. This is important because in a custom scrollbox we can easily change the parent class of TScrollBox to TALScrollBox
• Fixed the scrollbox movement when the user click in one ITextInput control inside the scrollbox, like TEdit
• Fix the bars in desktop to show when the mouse is over the scrollbox. This is how modern apps work, the scroll only appears when the mouse is inside the scrollbox.
• Fixed tracking with mouse in desktop, it was firing to movements at same time (the tracking (bars dragging) and the tap operations (mouse down, move, up))
• Added a small margins in bars by default to the bars don't "leave" the screen especially in maximized forms on windows
• Added possibility to change the bars position by the padding of the FContent. This is usefull because sometimes we have an control over the scrollbox (like a navigation menu) and we don't want the bars inside the navigation menu like any control of the scrollbox, then we can just set the FContent padding
• Fixed the pixel alignment of ViewportPosition