Add color for task

[dynobo]

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Added feature:
New option in config file "COLOR_ID" to add highlighting for the number at the beginning of every task line (the task id),

Steps for QA:

• Please test various combinations of highlightings with tasks containing numbers, and see if a formatting get's messed up

[dynobo]

Fixes #266

[karbassi]

@dynobo The priority highlighting works, but the numbers do no. See below with my tests.

Also, the test needs to have the numbers in front of the todo.txt

[karbassi]

@dynobo see my above comment.

[inkarkat]

Agree with closing; we've already accepted a more encompassing change.