Remove obsolete python code (<3.6).

[Natim]

No description provided.

[Glandos]

I personally love f-strings. They are cleaner, and on top of that, more performant at runtime.

But are we sure than we can expect all our user base to have python >= 3.6?

[Natim]

But are we sure than we can expect all our user base to have python >= 3.6?

Definitely yes. Python 3.5 endoflife is September 2020 and people can still use a previous version of I Hate Money in the meantime. Current Debian stable is Python 3.7

[Glandos]

And Python3.6 is available in CentOS7. OK, let's go.

[zorun]

As I already said in #421 and #475, I'm a bit sad about dropping support for Python 3.5 while both Python 3.5 and Debian stretch are still maintained (until September 2020 for Python 3.5, and until June 2022 for Debian stretch). But at this point, buster has been out for 9 months already so it's less annoying. I guess I'll just have to finally upgrade my server ;)
This will of course need to go in the upgrade notes for IHM 5.0.

@Natim btw, you seem to have missed a reference to python 3.5 in docs/installation.rst

[JocelynDelalande]

Ouch, I missed the conversation about it.

A bit sad also, because as yunohost is still on stretch, and it will stop ihatemoney_ynh from receiving ihm upgrades for a while for little actual gain (except dev ease).

But go ahead, yunohost will upgrade to buster soon, and it seems that I am a few months late for such an objection :). My bad