Rework getting subscriptions list

[UncleGoogle]

Should fix #165 #167

• more reliable source of username
• fix getting username for non-subscribers
• separate "not-yet-unlocked choice content" users from "never-subscriber" users in terms of fetching active content product machine name
• some refactors

[lgtm-com]

This pull request introduces 3 alerts when merging 43550df into 96e3214 - view on LGTM.com

new alerts:

• 2 for Unused import
• 1 for Wrong number of arguments in a call

[lgtm-com]

This pull request introduces 1 alert when merging f0f7316 into 046e1e3 - view on LGTM.com

new alerts:

• 1 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 1220301 into ffe063e - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 63c2997 into ffe063e - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 1 alert when merging 68ddfc9 into ffe063e - view on LGTM.com

new alerts:

• 1 for Unused import

[lgtm-com]

This pull request introduces 1 alert when merging 6adf13c into ffe063e - view on LGTM.com

new alerts:

• 1 for Unused import

[UncleGoogle]

to myself: continue WIP commit from trove_from_last_sub_strategy_draft