allow flags with backslash in append

https://github.com/mscdex/node-imap/issues/186
Merge pull request #299 from dominikgehl/dgl/flagsAppend

allow flags with backslash in append
esearch should call _esearch and return data to callback. Removed space in _esearch command and put it before encode, as query already has a space
Removed separate if for esearch result
Merge pull request #304 from ronniemb/master

esearch should call _esearch and return data to callback. Removed space ...
support for IMAP ID extension (RFC 2971)