Fix max preview, some resizing and caching issues and force preview providers to resize their previews properly

* introduces a method in OC_Image which doesn't stretch images when trying to make them fit in a box
* adds the method to all key providers so that they can do their job, as expected by the Preview class
* improves the caching mechanism of Preview in order to reduce I/O and to avoid filling the available disk space
* fixes some long standing issues
* **contains mostly tests**

6 files changed, 177 insertions, 0 deletions

diff --git a/tests/data/testimage-wide.png b/tests/data/testimage-wide.png
new file mode 100644
index 00000000000..144e0936576
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+++ b/tests/data/testimage-wide.png
diff --git a/tests/data/testimage.eps b/tests/data/testimage.eps
new file mode 100644
index 00000000000..8fa3ba44394
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diff --git a/tests/data/testimage.mp3 b/tests/data/testimage.mp3
new file mode 100644
index 00000000000..d2eea3cc4e5
--- /dev/null
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diff --git a/tests/data/testimage.mp4 b/tests/data/testimage.mp4
new file mode 100644
index 00000000000..1fc478842f5
--- /dev/null
+++ b/tests/data/testimage.mp4
diff --git a/tests/data/testimage.odt b/tests/data/testimage.odt
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index 00000000000..85646422d17
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diff --git a/tests/data/testimagelarge.svg b/tests/data/testimagelarge.svg
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