[WO-380] escaped quotes werent parsed properly

Gmail decodes doublequotes in mime encoded words when returning envelope data from IMAP

Actual header:

    =?UTF-8?Q?=22G=C3=BCnter__Hammerl=22?=

Gmail Envelope header in IMAP response:

    "=?ISO-8859-1?Q?\"G=FCnter__Hammerl\"?="

imap-handler failed to process escaped characters properly. Instead of returning the escaped char, backslash escape was returned instead

     "=?ISO-8859-1?Q?\\G=FCnter__Hammerl\\?="

which then resulted after decoding into

    "\\Günter  Hammerl\\"