Fixes #51

Refers to #35

This introduces a new optional configuration parameter called
"LogLevelMonitoring" to adjust the log level of those messages related
to the load monitoring of the service.

Fixes #50

Since we're now back on using a central location for storing temporary
transfer files, it does make sense again to check for that location to
exist on service startup (refers to #16).

This reverts commit 10640754.

Since this is not a common (central) location any more, it doesn't make
sense to check for it during startup or similar situations.

Megabytes have shown to be a bit clumsy in the configuration files, so
simply switch to the more useful Gigabytes unit.

Fixes #39

Allow setting the log level explicitly from "Warn", "Info", "Debug" or
"Trace" in the configuration.

Default is "Info", fallback for invalid settings is "Debug".

Fixes #34

Note that they are not included in the example configuration files as
these settings can easily mess up everything and should only be adjusted
with great care.

The default settings are valid on Windows 7 and Server 2012 and were
successfully tested on those versions.

Fixes #11

If a new directory is found in incoming but the move operation to
processing failed for some reason, the timestamp and username
directories (and potentially some partially moved data?) would remain
in processing. To prevent confusion about those "incomplete" transfer
candidates they are moved to the "ERROR" location.

Refers to #18

Refers to #18, #29

Refers to #18, #28, #29

Refers to #29

Refers to #28

Refers to #28

Refers to #28

Those objects are not meant to be instantiated directly but only using
the Deserialize() methods which takes care of creating a new object in
case deserializing fails for the status class.

This way the value is directly visible in the code where the property is
created, improving readability. Setting defaults in the constructor is
therefore not necessary any more.

Refers to #29

Refers to #18, #28

Refers to #29

Refers to #29

Refers to #29

Refers to #29

Refers to #29

Again, no functional changes in this commit!

Refers to #29

Plus, group them in a logical sequence instead of a type-specific one by
following the order being used in the new example files.

This commit should not introduce any functional changes!

Refers to #29

One file ("config.common.xml") containing site-global configuration
settings, the other one (the file name equals the host name with a
".xml" suffix) containing host-specific settings.

Both files use the same syntax and may contain the same setting
attributes with the host-specific one having priority over the
site-global one.

Refers to #18

They are already set by the XmlSerializer class to the default value of
the corresponding data type.