Fix invalid ChainID when it intersects with APDU boundary

[pscott]

This PR is based off of #636 's work. Unfortunately it's on a remote to which I don't have the access to, so I'm creating this PR with Hector's commit and building on top of it.
This PR:

• Fixes the problem when 4 byte chainID intesects with the APDU boundary
• Fixes the test apdus (since the first commit changes the way ledgerjs generates apdus in certain cases).
• Rename rlpOffset to vrsOffset to code readibility.

Closes #636

[codecov]

Codecov Report

Merging #644 (5899789) into master (031cf51) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #644   +/-   ##
=======================================
  Coverage   40.93%   40.93%           
=======================================
  Files          74       74           
  Lines        4397     4397           
  Branches      720      720           
=======================================
  Hits         1800     1800           
  Misses       2580     2580           
  Partials       17       17           

Impacted Files	Coverage Δ
packages/hw-app-eth/src/Eth.ts	85.84% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 031cf51...5899789. Read the comment docs.