Fixes #56

Fixes #53

Fixes #55

Fixes #54

Refers to #50

That's the earliest place where setting up the mail logger is possible /
makes sense, so do it right then. Additionally, the check for SmtpHost
is redundant since it also done in the method called, so no need for it.

Refers to #50

Refers to #35

This reverts commit 3f7fd9dc.

As intended and announced in the previous commit message.

Relates to #20

NOTE: this is known to fail for permission reasons, the commit is in
fact just to save the code and serve as an example (and to be reverted
right away).

Relates to #20

This way the service should now finally receive the system shutdown
events and be able to properly shut itself down.

Fixes #45

Fixes #41

Fixes #47

If users don't have the permissions to scan a folder hierarchy, they're
not supposed to transfer it anyway - so just show an error message.

Fixes #48

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

This prevents at least the log file from being cluttered up completely
in "normal" operation. As stated in #50 the level for those messages
should be configurable to allow for easy adjustments without the need to
recompile the service itself.

Otherwise AutoTx will try to process them in each iteration but fail
right away, thus blocking all other transfers while the dir is there.

Fixes #49

Fixes #38

In addition to the previously added package name / path, the marker file
now gets populated with the following:

- host name (redundant, but easy to parse from here)
- the time stamp when the update happened
- build commit
- build configuration

The encoding of the file is changed to be ASCII, otherwise PowerShell always
places the ugly BOM (byte-order-mark) at the beginning, confusing a lot of
editors.

Fixes #46

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.