Release schedule for 0.15.0

[laanwj]

Here is a proposed release schedule for 0.15.0. Like for previous major releases I've added 6 months to the previous release schedule (#8719).

2017-07-02
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- Open Transifex translations for 0.15
- Soft translation string freeze (no large or unnecessary string changes until release)
- Finalize and close translations for 0.13

2017-07-16
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- Feature freeze (bug fixes only until release)
- Translation string freeze (no more source language changes until release)

2017-08-06
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- Split off `0.15` branch from `master`
- Start RC cycle, tag and release `0.15.0rc1`
- Start merging for 0.16 on master branch

2017-09-01
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- Release 0.15.0 final (aim)

If any specific dates or timeframes are a problem, let me know.