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.
Fix possible crash after migrate of mbox to maildir

Folders can leave notifications in the main loop which would be delivered
on idle, but these can be left in the main loop longer than the temporary
CamelSession object is alive, which leads to a crash, because of
the CamelStore's descendant being freed too early.
tests: capture stdout
tests: don't use pkexec
tests: correctly calculate combobox/textbox pair