RFR: JDK-8237845 Encapsulate doclet options

[Jonathan Gibbons]

Please review a conceptually simple review to encapsulate the fields 
holding the values of doclet options, in the BaseOptions and HtmlOptions 
classes.

The encapsulation was done with an IDE. The fields are all changed to 
private access; the access methods are package-private by default, and 
public when necessary, although in general, there is no problem if it is 
determined they should all have public access.  This is the same policy 
as was done for ToolOptions, currently in review.

Some fields need public "setters". These were added manually.

In a few places, code was simplified manually, joining short lines, or 
replacing `configuration.getOptions()` with just `options`.

This is intended to be the last in the current round of option-code 
cleanup, for now, although I think there is scope for future work to 
rationalize the names of the fields and corresponding accessor methods.

-- Jon


JBS: https://bugs.openjdk.java.net/browse/JDK-8237845
Webrev: http://cr.openjdk.java.net/~jjg/8237845/webrev.00/