Remove all trailing spaces

No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.

This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.

interface/wx/html/htmlcell.h

@@ -8,7 +8,7 @@
 
 /**
    @class wxHtmlRenderingStyle
- 
+
    wxHtmlSelection is data holder with information about text selection.
    Selection is defined by two positions (beginning and end of the selection)
    and two leaf(!) cells at these positions.