update main with backend changes

changes:

• containers uniformly named like lvlXX-cYY
• no level-specific bridges
• rather, containers use profile "hacklab" + IP addres (CIDR/24)
• still, lxdbr0 provides IPs via DHCP ( -> alpine iso )
• logs are managed by log.sh

to dos:

• implement shell template from Prof. Thielen ?

Closes #63 (closed)