Add battery contact Keystone 261

[mibe]

Keystone 261 is a battery contact for 9 volt PP3 batteries.
Datasheet

Screenshot:

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I prefixed the footprint with BatteryContact_ as discussed in #2149.

The datasheet does not have a recommended PCB layout. I used the max. part diameter (7.92 mm), added 0.5 mm to the radius and rounded the resulting diameter up to 9 mm, and used this value for the pad size. The part fits quite nicely on this:

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KLC violations:

• F5.1: The footprint has no simplified outline on the silk layer, since it would be exposed on the pad.
• F5.1: There is no pin 1 designator because this footprint has only one pad. A designator would be futile.
• F5.2: There's again no pin 1 location drawn due to the same reason as above.

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All contributions to the kicad library must follow the KiCad library convention

Thanks for creating a pull request to contribute to the KiCad libraries! To speed up integration of your PR, please check the following items:

• Provide a URL to a datasheet for the footprint(s) you are contributing
• An example screenshot image is very helpful
• If there are matching symbol or 3D model pull requests, provide link(s) as appropriate
• Check the output of the Travis automated check scripts - fix any errors as required
• Give a reason behind any intentional library convention rule violation.

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Be patient, we maintainers are volunteers with limited time and need to check your contribution against the datasheet. You can speed up the process by providing all the necessary information (see above). And you can speed up the process even more by providing a dimensioned drawing of your contribution. A tutorial on how to do that is found here: https://forum.kicad.info/t/how-to-check-footprint-correctness/9279 (This is optional!)

[strfry]

Keystone 269 should also be included for practical value of this PR?

[mibe]

@strfry there's #2182 for the 269 part.
Or did you mean to include the 269 part in this PR?