Add general script with helper functions

[chros73]

Add general rtUtils.sh script with helper functions that can be included into main scripts:

• should compose and send email with the help of ssmtp util
• add generic addMsg, writeHelper, sendEmail functions
• should check mount point with checkMountPoint function (with cookies)
• should check free space on device and should report it
• should check if rtorrent is running, if not then it starts it in tmux (with cookies)
• should be able to enable/disable certain parts of it

Additional tasks:

• add the necessary cookie file as well
• modify ssmtp config to be able to work with a gmail account