[Lazarus] Hint of TAChart

[Werner Pamler]

You are probably working with DistanceMode=cdmOnlyX of the 
DataPointHintTool; with cdmOnlyY the hint would appear if the mouse is 
at the left or right outside the series region.

I am not sure if this is really a bug, but I can imagine that users 
could be surprised by this behavior. Therefore, I added a new property 
"MouseInsideOnly" to TDatapointHintTool and TDatapointCrosshairTool (in 
fact, it is implemented already for their ancestor TDataPointTool, but I 
think the other datapoint tools do not need it). With "MouseInsideOnly" 
set to true the hint does not appear if the mouse is outside the 
plotting frame.