* GSN support
Add base Context contract
Add GSNContext and tests
Add RelayHub deployment to tests
Add RelayProvider integration, complete GSNContext tests
Switch dependency to openzeppelin-gsn-provider
Add default txfee to provider
Add basic signing recipient
Sign more values
Add comment clarifying RelayHub's msg.data
Make context constructors internal
Rename SigningRecipient to GSNRecipientSignedData
Add ERC20Charge recipients
Harcode RelayHub address into GSNContext
Fix Solidity linter errors
Run server from binary, use gsn-helpers to fund it
Migrate to published @openzeppelin/gsn-helpers
Silence false-positive compiler warning
Use GSN helper assertions
Rename meta-tx to gsn, take out of drafts
Merge ERC20 charge recipients into a single one
Rename GSNRecipients to Bouncers
Add GSNBouncerUtils to decouple the bouncers from GSNRecipient
Add _upgradeRelayHub
Store RelayHub address using unstructored storage
Add IRelayHub
Add _withdrawDeposits to GSNRecipient
Add relayHub version to recipient
Make _acceptRelayedCall and _declineRelayedCall easier to use
Rename GSNBouncerUtils to GSNBouncerBase, make it IRelayRecipient
Improve GSNBouncerBase, make pre and post sender-protected and optional
Fix GSNBouncerERC20Fee, add tests
Add missing GSNBouncerSignature test
Override transferFrom in __unstable__ERC20PrimaryAdmin
Rhub address slot reduced by 1
Rename relay hub changed event
Use released gsn-provider
* move gsn to all caps
* update to gsn contracts in solidity/master
* Adapt for ethereum-package
* update gsn related packages
* update dependencies to match contracts repo
* remove mocha bail option
* add changelog entry
* add constructors to mocks
* use unstructured storage for bouncer implementations
