Minor additions on the dashboard

[greenward]

Hi, as I said to you in discord, this are the changes that I did on the dashboard files:

• added clean memory script to clean buffers/cache and swap every hour;
• removed lm-sensors dependency for temp, used vcgencmd measure_temp, which is built in;
• mounted miner logs to /home/pi/hnt/miner/log which permits the dashboard to have access to it without issueing docker commands;
• added the removal of the older docker images when upgrading with success the version;
• added the /etc/lsb_release update when there is a new firmware version. This file is responsible to show the firmware version on helium app.