Check and fix various inconsistencies

[Studio384]

While designing Valkyrie, the way icons were drawn has been highly inconsistent. Recent icons started using the round line cap as it should, but various icons don't use it. Our roundings are also highly inconsistent due to random usage of inner, centered and outer borders.

This issue is about reworking icons to match the following guidelines:

• The stroke alignment MUST be set to centered.
• The cap style MUST be set to rounded.
• The join style MUST be set to round.

In part this should greatly reduce the post-flattened changes that we have to make to icons.