Add battery contact Keystone 269

[mibe]

Keystone 269 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 which is flush with the PCB (6.35 mm), added 0.5 mm to the radius and rounded the resulting diameter up to 7.5 mm, and used this value for the pad size.
The datasheet states that the anti-rotation dimples are at a random location, but the photos at DigiKey and the parts I ordered all had the dimples at 45° and 225°, so I positioned the drill holes at this position, to make the outline on the fab & silk layer fit to the part.

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KLC violations:

• 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!)