[debabsah]

Sets the version to 0.5.0 and dates the changelog.

0.5.0 contains:

• the UI-added chart fix (A chart added in Superset no longer breaks apply on 4.1 and 5.0 #26);
• adopt in place (Adopt a dashboard built in the UI in place #27);
• decompile naming the settings it drops, and the 6.1 subtitle (Decompile names the settings it drops instead of dropping them silently #28);
• connection retries (Retry once a GET or PUT the server dropped unanswered #29, Resend a dropped chart query too, since it only reads #33);
• backups that record their instance, prune themselves and clean up orphans after a restore (Backups record their instance, restore cleans up orphans, old backups are pruned #30);
• the fixable flags on the window rules (Mark the two window rules fixable, and test the registry against what rules emit #31);
• saved queries for CSV reports (Save each chart's query as Superset's Save does, so CSV reports work #32);
• stacked charts read back as a sketch (Decompile reads stacked charts back as a sketch instead of flattening them #34).

The live audit is held back pending the premium-line decision (fleet decision #11). The changelog's "Upgrading from 0.4" section lists what changes for existing users. Offline: 1547 passed, 1 skipped.