Remove reference to project board

We haven't been using it to set priorities for a while now.

Remove link to dead todo repository

Replace references to repo name `xjava` with references to repo name `java`

all-your-base: update to v1.1.0 of tests

Remove leading 'x' from repository name

The leading 'x' is kind of arbitrary. Especially now that we can set
topics on the repositories, we don't need a pattern to distinguish what
is a track or not.

The repository itself has already been renamed. GitHub redirects from
the old name to the new name, so we do not have to rush to fix links to
the old repository name, though we should update them for the sake of
clarity.

I chose to skip the x-common test case "both bases are negative" since
the xjava implementation of this exercise forces the first base to be
validated before a second base can be supplied. This test would
therefore be redundant since we already have tests that validate the
first base.

Removing final from starter classes

Add policy for 'final' classes

run-length-encoding: estimate difficulty 5

Clean up root build script

Update Gradle wrapper to 4.0

kindergarten-garden: estimate difficulty 4

hello-world: explain @Ignore annotations

scrabble-score: update to v1.0.0 of tests

Add cross-referencing comments r.e. stripping ignores