move general connection methods into own class
Move fetch-timer methods to own class
remove unnessary use of a unique pointer
move header decoder methods to own class
improve code formatting
move generic imapclient part to own tranlation unit
move net client application level to translation unit
split copy client classes into translation units
make callback members protected
allow equal signs without following question mark

in headers - where '=?' marks the begin of an MIME encoded word