Create short unique identifier for ecoinvent releases

[cmutel]

SPDX provides widely-used identifiers for licenses. We need the same thing for ecoinvent releases (e.g. 3.8 + APOS) which are short, unique, and also widely-used and accepted.

Advantages:

• This could become the default database name when importing
• Allows us to look up additional metadata on the ecoinvent website
• Skip one annoying step in data portability

[jsvgoncalves]

ei-<version>-<system-model>

# versions
3.8                                                                                                                                                                                          
3.7.1                                                                                                                                                                                        
3.7                                                                                                                                                                                          
3.6                                                                                                                                                                                          
3.5                                                                                                                                                                                          
3.4                                                                                                                                                                                          
3.3                                                                                                                                                                                          
3.2                                                                                                                                                                                          
3.1                                                                                                                                                                                          
3.01                                                                                                                                                                                         

# system models                                                                                                                                                                                
EN15804                                                                                                                                                                                      
apos                                                                                                                                                                                         
consequential                                                                                                                                                                                
cutoff