Removed hard-coded path to ical2rem-cli.

Script now requires ical2rem-cli to be in the PATH.
Added full paths to commands and files.

The shell that cron runs scripts in runs them from the user's home directory,
not the directory with the script, so relative paths must account for that.
This was causing the script to not be able to find the calendar_list file.

The script run by cron also does not have the same PATH as the normal user.
This was preventing the script from finding the ical2rem-cli and org2remind.pl
files.  For now, their full paths have been hard-coded in.  Ultimately, they
(and the location of the calendar_list) file can be set in configuration
variables.
Change wget to not print any output.

The -nv flag still printed output for each file that was downloaded, which is
not needed in the normal case (plus it puts the URLs for the calendars in more
locations).  This would not print error information, but wget does not provide
any additional output if an attempt is made to download a URL that does not
exist.