Implement DOM range iterator.

[Martin Kou]

#2864 and #2865 depends on DOM range iterator to work. So the DOM range iterator must be implemented first as a separate plugin.

[Martin Kou]

This patch also adds trim(), ltrim() and rtrim() under CKEDITOR.dom.node. Also it moved getFirst() and getLast() to CKEDITOR.dom.node, as those functions may be used outside of elements.

[Martin Kou]

Fixed a bug which causes JavaScript errors in CKEDITOR.dom.node::rtrim().

[Martin Kou]

Another update - refactored the block boundary checking logic in dom walker to CKEDITOR.dom.element::isBlockBoundary(), since both the dom walker and the dom iterator code need it. Also, it's found to be needed by the list (#2864) and indent (#2865) plugins being developed.

[Frederico Caldeira Knabben]

• The "domiterator" is the kind of plugin that don't have to go inside the plugins configuration. It's loaded only if we have other plugins that depend on it.

• As I could note, things have been copied from V2 as is, with no adaptation to V3. It means we'll have to work more on this code later.

• There was a reason for having getFirst and getLast inside element, and not on node. Actually, they are not useful outside the element scope. For example, "textNode.getFirst()" means nothing. I don't care about the W3C DOM here, as our intention is not to implement it. We have a custom implementation that can be clearer, and so we should avoid such DOM generalities. If part of our code is supposed to do "textNode.getFirst()", then our code must be fixed, as it only impacts on performance, as we know it'll never return a node. Anything that's element specific must go inside the element class only.

[Martin Kou]

Fixed with [3050].