* Problem: No docs explaining use of MongoDB for querying
Solution: Start a new root docs page explaining how a node operator can use the full power of MongoDB's query engine, and can expose as much of that as they like to end users.
* Finished first draft of new docs page 'Querying BigchainDB'
* Combining configs
* Combining the persistent volume claims into a single file.
* Combining the storage classes into a single file.
* Updating documentation
* Multiple changes
* Support for ConfigMap
* Custom MongoDB container for BigchainDB
* Update documentation to run a single node on k8s
* Additional documentation
* Documentation to add a node to an existing BigchainDB cluster
* Commit on rolling upgrades
* Fixing minor documentation mistakes
* Documentation updates as per @ttmc's comments
* Block formatting error
* Change in ConfigMap yaml config
* Fix typos pointed out in review by @ttmc
* Reword description of an input in the transaction schema
* Re-add removed comment in transaction model
* Fix small typos in some comments in the transaction model
* Add trailling commas to a multiline dict in the transaction model tests
* Fix small things with server docs changes
* Add description of public keys' association with conditions in transaction concept docs
* Reword description of Transaction.create's and args
* Rename output_uri to output_condition_uri
* Fix hardcoded class name vs. self.__class__
* Rename instances of 'out' with 'output'
* Rename instances of and with to avoid name clash with built-in
* Remove unnecessary renaming of cryptoconditions.Fulfillment import in transaction model
* Remove instances of in transaction model
* Remove usages of fulfillment in cases where input makes more sense
* Reword docstrings for init methods in transaction models
* Rename usages of condition where output is now a better fit
* Add descriptions to TransactionLink's txid and idx in schema
* Minor correction to output idx description in transaction yaml
