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**

1 files changed, 2 insertions, 0 deletions

diff --git a/tests/data/testimagelarge.svg b/tests/data/testimagelarge.svg
new file mode 100644
index 00000000000..2d505c4db0f
--- /dev/null
+++ b/tests/data/testimagelarge.svg
@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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