vlconv: Make parsing loops check env.IsCancelled()

Make it possible to abort during parsing loops.
If aborted delete the written file.
Volkslogger flight download. Prepare xcs code to call Logger.cpp

New Logger.cpp contains functions for flight download.
build/driver.mk updated.
Register.cpp added flag for flight download capability
Volkslog:Implement first_char timeout, let readdir return data_length

When the command to download the the main flightlog
data is send to the VL it starts calculating security.
Therefore the reply to the first ACK takes very long.
For this reason a special timeout for the first char
had to be implemented in the ReadBulk() routing and
subsequently in the routines SendCommandReadBulk() as
well.
Also let readdir() return the length of the read data
so it can be passed to conv_dir to fix the parsing
bug there.
Volkslogger: Fix conv_dir()

conversion from raw binary format to flight list
(directory) was failing due to bad end condition
of parsing loop. See comment.
Implemented data_length parameter to end loop
at the right spot.
vlapi:Replace new/delete by std::vector

The line with delete[] caused a segmentation fault.
The new/delete[] was replaced by switching to
std::vector.
Also changed the return type of conv_dir to
std:vector<DIRENTRY> to make the whole api a little
easier to read.
VLAPI:Reduce calling conv_dir to one time

Since we have conv_dir() now using std::vector.
The first "count only" call of the function is
no longer necessary.
The original use was to determine the count of
entries so the dynamic array could be initialized
with the correct size. std::vector makes that 
obsolete.
vlapi: Create log directory if necessary

Opening the logfile with _tfopen() fails if
the log directory is not existant in the
XCSoarData Folder.
If it is not there create it.
vlapi: Implement Bulkrate

Make Bulkrate configurable from UI.
This Bulkrate applies only to the download of 
the actual flight log.
The download of the flight list (called DIRECTORY)
and the signature have to be carried out with 
standard IO Rate 9600 baud
vlapi: Enhance progress bar functionality

Create a cyling progress bar.
Since the amount of data is not known before
transmission it is not possible to create
a single progress bar which would run from 0
to 100 %
vlapi: Generate user message to wait for Volkslogger

To make the user aware of the Volkslogger taking time
to calculate file security a message is generated.