consensus,store: enforce block size limits, compact serializations, misc badger fixes

[jchappelow]

The PR starts with enforcing the consensus parameter (in genesis.json) for max block size.

This also led to several changes in block and transaction serialization, primarily the use of variable length integers in length-prefixed data, which includes many fields in the transaction and transaction body. None of the payloads that JS would have to serialize are changed. The size of a block with many fairly small transactions is drastically reduced.

The SerializeSize methods are added or improved, as these are required for efficient size checks without actually allocating huge amounts of memory.

Finally, this addresses some minor issues related to the block store:

• much of the config was not working as intended, namely the logger was being overriden
• our default of no-compression (an override from badger defaults) did not set badger's internal "block" cache to 0 (disabled) which the badger docs recommend if no compression or encryption are used
• expose a store.compression option

Related: #1347