EHTMLEditorView: Replace Tab character with 8 spaces instead of 4
EHTMLEditorView: Skip BR on the end of HTML that's parsed into paragraphs

Do that to avoid unnecessary empty paragraph element.
EHTMLEditor: Fix various bugs in block in/undent

Fix the wrong position of caret when in/undenting empty block and don't
lose spell checked words when in/undenting. Also don't insert unnecessary empty
lines into plain text version of message when processing indented block.