Default keep revisions to disabled, and remove tests for revisions

This commit sets the "keep revisions" setting to disabled by default
for new projects.  It also removes the test cases associated with
revisions.

The revisions feature as currently implemented is of questionable use.
It has been a source of performance issues for users, and has consumed
developer time in attempts to address its shortcomings.  This commit
is the first step to deprecate the current revisions feature.

manuskript/settings.py

@@ -85,7 +85,7 @@
     }
 
 revisions = {
-    "keep": True,
+    "keep": False,
     "smartremove": True,
     "rules": collections.OrderedDict({
         10 * 60:            60,                     # One per minute for the last 10mn

manuskript/tests/models/test_outlineItem.py

@@ -59,9 +59,6 @@ def test_outlineItemsProperties(outlineItemFolder, outlineItemText):
     text.setData(text.enum.goal, 4)
     assert text.data(text.enum.goalPercentage) == .5
 
-    # revisions
-    assert text.data(text.enum.revisions) == []
-
 def test_modelStuff(outlineModelBasic):
     """
     Tests with children items.
@@ -126,16 +123,6 @@ def test_modelStuff(outlineModelBasic):
     assert folder.findItemsContaining("VALUE", cols,  MW, True) == []
     assert folder.findItemsContaining("VALUE", cols,  MW, False) == [text2.ID()]
 
-    # Revisions
-    text2.clearAllRevisions()
-    assert text2.revisions() == []
-    text2.setData(text2.enum.text, "Some value.")
-    assert len(text2.revisions()) == 1
-    text2.setData(text2.enum.text, "Some new value.")
-    assert len(text2.revisions()) == 1  # Auto clean
-    text2.deleteRevision(text2.revisions()[0][0])
-    assert len(text2.revisions()) == 0
-
     # Model, count and copy
     k = folder._model
     folder.setModel(14)