The active probability estimator can be switched dynamically using the
`Set/GetMissionControl` API, maintaining backward compatibility. The
lncli commands `setmccfg` and `getmccfg` are updated around this
functionality. Note that deprecated configuration parameters were
removed from the commands.
This commit also introduces `mppTestScenario` which replaces the old
`mppmppTestContext` to reduce the total blocks mined during the test.
For each test case it will save 35 blocks.
This commit starts the construction of the new package `lntemp`. This
package serves as the scaffolding while we migrate our old itest into
the new one. Once the migration is finished, the package will be put
back to `lntest`.
