Fix handling of little-endian date format

Ever since version 2.0, when parsing a journal file, jrnl would not use
the custom date format string anymore. Instead, it relied on the
dateutil library to get the parsing right. This change was made to allow
people to change their date format without having to manually change
their file. However, this broke some existing date formats like
%d.%m.%Y, as it would falsely interpret the month as day and vice versa.
This commit adds some tests to catch this error and fixes it by trying
to parse the dates using the custom format first, only falling back to
dateutil when needed.

features/data/configs/little_endian_dates.yaml

@@ -0,0 +1,12 @@
+default_hour: 9
+default_minute: 0
+editor: ""
+encrypt: false
+highlight: true
+journals:
+  default: features/journals/little_endian_dates.journal
+linewrap: 80
+tagsymbols: "@"
+template: false
+timeformat: "%d.%m.%Y %H:%M"
+indent_character: "|"

features/data/configs/upgrade_from_195_little_endian_dates.json

@@ -0,0 +1,11 @@
+{
+"default_hour": 9,
+"timeformat": "%d.%m.%Y %H:%M",
+"linewrap": 80,
+"encrypt": false,
+"editor": "",
+"default_minute": 0,
+"highlight": true,
+"journals": {"default": "features/journals/simple_jrnl-1-9-5_little_endian_dates.journal"},
+"tagsymbols": "@"
+}

features/data/journals/little_endian_dates.journal

@@ -0,0 +1,5 @@
+[09.06.2013 15:39] My first entry.
+Everything is alright
+
+[10.06.2013 15:40] Life is good.
+But I'm better.

features/data/journals/simple_jrnl-1-9-5_little_endian_dates.journal

@@ -0,0 +1,13 @@
+10.06.2010 15:00 A life without chocolate is like a bad analogy.
+
+10.06.2013 15:40 He said "[this] is the best time to be alive".
+Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent malesuada
+quis est ac dignissim. Aliquam dignissim rutrum pretium. Phasellus pellentesque
+augue et venenatis facilisis.
+
+[03.08.2019 12:55] Some chat log or something
+
+Suspendisse potenti. Sed dignissim sed nisl eu consequat. Aenean ante ex,
+elementum ut interdum et, mattis eget lacus. In commodo nulla nec tellus
+placerat, sed ultricies metus bibendum. Duis eget venenatis erat. In at dolor
+dui.