minor improvements in terminology, csv input

* renamed a few vars that might be confusing, e.gmatureBlock -> startBlock
* fixed a off-by-one in the csv input - matched the block height and no of
transactions
* updated starting block to 15000 as the difficulty at that height seems
stable enough to control mining
IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.