FAB-12836 #done

Change-Id: I93d55fb4dc07a92a4cd082fb6ecb285381bd8783
Signed-off-by: manish <manish.sethi@gmail.com>

    This CR includes
     - Introducing a proto message for encapsulating the version
       and metadata for persisting both in the ~version field
     - Enhancement to the encoding/decoding so as to handle both
       the old and new format of encoding of the ~version field

Change-Id: Ica55f7af1206deeee4d93ae89d9a9045b30a8d26
Signed-off-by: manish <manish.sethi@gmail.com>
Signed-off-by: Matthias Neugschwandtner <eug@zurich.ibm.com>

Part 1 of ledger servicebility improvement:
Update core/ledger/kvledger to use error handling framework

Change-Id: I8415f88d64e47537c4f9e863f10eeb7846082e89
Signed-off-by: Wenjian Qiao <wenjianq@gmail.com>

The key for CouchDB documents cannot begin with an underscore.

This change adds validation in simulation and commit to prevent the
key from beginning with an underscore.

Remove the ~metadata restriction.

Documentation is updated to reflect the change.

Change-Id: I7a0bb9e0af9e513a982806693e64d18fae226d2d
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>

Ledger removed the "data" wrapper when using CouchDB as the
state database.  This change means that documents in the state
database must meet CouchDB's restrictions for top level field
names.

The validation for simulation and commit needs to be updated
for the following invalid field names:

- Any field beginning with an underscore, "_"
- ~version
- ~metadata

Change-Id: I9203691553de8c15888ce93ade99337bad5222a9
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>

Unmarshaling a the string "null" results in a nil which is
unexpected by statecouchdb.  This causes a downstream failure.

This change adds handling for the special case of string "null".

Change-Id: I37cd5c07a6da42a37b441225e809de8c9f0c1d93
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>

This CR refactors the code for statecouchdb implementation.
This includes splitting the code into different files and
making the code more modular by spliting it into high level structures and functions
so to make the code more readble and maintainable

The unit tests are not changed in this CR so as to make sure
that things are not lost in the refactoring

Change-Id: I5c937f7d3c541be0b89591175b6946ae32c5833f
Signed-off-by: manish <manish.sethi@gmail.com>