statistics: add statistic variables

The StatisticVariable class hierarchy encapsulates the concept
of a dive-variable, which can be plotted in charts either as
dependend or independend variable.

There are three types of these variables:
1) discrete: For example dive buddies or suit type.
2) continuous: Has a notion of linear metric - can be
   used as histogram or scatter plot axis.
3) numeric: Like continuous, but allows for operations
   such as calculating the mean or the sum over numerous
   dives.

All variables support binning. The bins are defined per
variable.

Continuous variables can be converted into an arbitrary
double value, which is used to be plotted on a continuous
axis.

Moreover, numeric variables support a number of operations,
which depend on the variable.

Since binning is based on different types, the code is rather
template-heavy. Of course, this could be solved with
unions/variants and runtime-polymorphism, but using templates
was just much quicker. Notably, this uses the CRTP
(curiously recurring template pattern) where a subclass
passes itself as argument to the baseclass. This is a weird
kind of "reverse inheritance".

The StatsTranslations class is a dummy class which will
be used to collect all translations of the statistics
module.

This includes changes by Dirk to fix compilation of the
downloader.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/stats/statstranslations.h b/stats/statstranslations.h
new file mode 100644
index 000000000..dadfc83af
--- /dev/null
+++ b/stats/statstranslations.h
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+// Dummy object for stats-module related translations
+
+#ifndef STATS_TRANSLATIONS_H
+#define STATS_TRANSLATIONS_H
+
+#include <QObject>
+
+class StatsTranslations : public QObject
+{
+	Q_OBJECT
+};
+
+#endif