Support 2mln assets portoflio (Sparse Vectors)

[sadhbh-c0d3]

• Implement selective Load / Store from StorageMap
• Update VIL programs to use selective Load / Store instead of Join-xxx operations

At present VIL loads (and stores) full vectors from Blockchain, which has size limitation. If we want to support infinite portfolio size, then we must use mapping to store it, and be able to load (and store) from that mapping. VIL programs operate on vectors (because it's all vector algebra), and that is great, but we need to be able to produce a vector from select elements of mapping, so that we just match Index assets with portoflio. This simple fix will enable unlimited number of assets in portfolio.