PoC: smart legal contract (.slc) format with contract signing

[jeromesimeon]

Signed-off-by: jeromesimeon [email protected]

Changes

• Reduce dependency of (contract) instances to templates so they can be created more independently
• Add fromTemplate method to create an instance from a template
• Rename instance classes for clarity
• Adds initial instance loader and instance saver with ability to create a .slc smart legal contract archive
• Adds support for SLC execution
• Adds support for SLC export to different format
• Adds contract signing support (Contributed by @sanketshevkar)

Flags

• Implements part of the notion of smart legal contract document, as discussed in Issue #677
• Nothing fundamentally new in this PR, but this is a clean replacement for #679 which includes contract signing (contribution by @sanketshevkar during GSoC)

[coveralls]

Coverage decreased (-0.6%) to 96.682% when pulling de62bc8bff7128607dae7cd7187a72b343bbab4d on poc-slc into 719594c11be69db165fbdb6a95bc917d991da49c on master.