-l|--prefix-location (p)wd|(g)it|git-(s)uper|(u)ser|(S)ystem

for `duct` and `con-duct ls` and likely others.

ATM we by default use `.duct/logs/` from current directory as the default location where to store our logs.

In principle we do provide means to alter that but it is "too verbose" since requires them modification of the full prefix.

For #170 and overall use within/under git we might want to place them under root folder of the git repository where it is executed.

My most frequent desire/use ATM is desire to just store them user-wide (platformdir python module could be used to determine location cross platforms), e.g. under `~/.var/duct/logs` since e.g. I am not the owner of the folder where I am running the command or just this folder temporary but logs would be valuable longer term etc.

Hence proposal for an option to be able to quickly alter the folder to use instead of `.duct/logs/` within prefix. Short version should be concise and thus e.g. `-l u` should store under user wide folder, and `-l S` some system wide (user might have some permission set there)

note: whenever we store somewhere else, we better also store pwd folder -- might need to be relative or might be full path... yet to be decided