Refactor lazy sync code

[Zebradil]

This PR:

• simplifies lazy sync flags handling
• correctly handles os.Stat errors in some places
• removes not needed functions
• fixes spelling

For a reviewer: checking every commit separately may be easier, as the changes are grouped logically.

[kumaritanushree]

For a reviewer: checking every commit separately may be easier, as the changes are grouped logically.

@Zebradil this really makes easy in reviewing changes. Thanks Changes looks good to me. Lets wait for @joaopapereira approval.