Clamscan Monitoring Plugin

The plugin checks various scenarios:
-the last scan was too long ago
-the current scan runs too long (e.g. clamscan hangs on an infected file)
-an infected file is listed in the scan summary
-the scan summary log could not be parsed correctly
-the scan summary log could not be opened by the plugin for parsing (e.g. plugin is not called with the correct log file path)
-If clamscan is currently running, the pid of the process is printed
-If the scan output could be parsed successfully, the engine version and the performance data of the scan are printed

Requirements
The plugin raises an error if it cannot find clamscan with 'which clamscan'.

Required perl modules
* use Getopt::Long qw(:config no_ignore_case);
* use Proc::ProcessTable;
* use File::stat;
* use Switch;
* use Date::Calc qw(Delta_Days);
* use Date::Calc qw(Delta_DHMS);
* use Date::Calc qw(Localtime);