Summarize a month of Geotab billing by plan and database

**Objective:** Summarize device billing for month {month} of year {year} (both default to the current period when blank), optionally limited to database {database}.

**Step 1: Charges**

Call `geotab-myadmin-get-device-contract-transaction` with month = {month}, year = {year} and, if given, database = {database}. Use a max-records high enough to cover the month (for example 1000); if the result hits that cap, say the totals are partial.

**Step 2: Credits and termination fees**

* Call `geotab-myadmin-get-device-contract-credit-transaction` with the same month and year.
* Call `geotab-myadmin-get-device-contract-early-termination-fee` with the same month and year.

**Step 3: Report**

* Totals: charges, credits, early termination fees and net, in local currency and USD where available.
* A table of charges by rate plan: device count, total value.
* If no database filter was given, a table of charges by database.
* The 10 largest single charges.

**Rules & Guidelines:**

* This is a read-only job. Do NOT call any write tool: no `geotab-myadmin-change-device-billing-plan`, `geotab-myadmin-terminate-device-billing`, `geotab-myadmin-share-device`, `geotab-myadmin-update-device-contracts`, `geotab-myadmin-enroll-device-from-add-in`, `geotab-myadmin-unenroll-device-from-add-in` or any other action tool.
* Do not mix currencies in one total; group by currency if there is more than one.

**Validation:**

* If all three reads return nothing, say there is no billing for the period and stop.