Reduce the memory used by DOM variables

Free some of the DOM variables when they are not needed, before they are
automatically freed when the frame is destroyed
EHTMLEditorSelection - Fix the spell check after settings alignment
EHTMLEditorSelection - Fix the unindentation of the list
EHTMLEditorSelection - Limit the paragraph minimal width to 5 characters
EHTMLEditorSelection - Remove just the BR elements that are used for the wrapping unless it is forced
EHTMLEditorView - Turn on the spell check if the inline spelling option is set

Otherwise the spell check is not forced when the message is loaded into
the composer.
EHTMLEditorView - Remove the unneeded comment
EHTMLEditorView - Process the plain text version the right way when sending the HTML mail