* sync: Validate received BlockHeaders packets against stored request.
* sync: Validate received BlockBodies and BlockReceipts.
* sync: Fix broken tests.
* sync: Unit tests for BlockDownloader::import_headers.
* sync: Unit tests for import_{bodies,receipts}.
* tests: Add missing method doc.
* Update `add_license` script
* run script
* add `remove duplicate lines script` and run it
* Revert changes `English spaces`
* strip whitespaces
* Revert `GPL` in files with `apache/mit license`
* don't append `gpl license` in files with other lic
* Don't append `gpl header` in files with other lic.
* re-ran script
* include c and cpp files too
* remove duplicate header
* rebase nit