Base: simplify UnitsSchemas management

Fixes: Maintaining schemas is difficult and error-prone

- Facilitate easy schemas add, remove, change, etc.
- Remove 14 files containing approx 2,190 lines of if/else code and data
- Place data in one file (UnitsSchemasData.h) using a normalized structure (including special functions)
- Isolate and simplify data operations (code)
- Remove schemas enum to keep data independent of code
- Separate responsibilities: Specifications, data, schemas, schema
- Add schema data 'isDefault'
- Add schema data name
- Prefer algorithms to raw loops
- Add schemas unit tests
- Tweak quantity unit tests

src/Gui/QuantitySpinBox.cpp

@@ -45,6 +45,7 @@
 #include <Base/Exception.h>
 #include <Base/UnitsApi.h>
 #include <Base/Tools.h>
+#include <Base/UnitsSchema.h>
 
 #include "QuantitySpinBox.h"
 #include "QuantitySpinBox_p.h"
@@ -714,7 +715,7 @@ void QuantitySpinBox::setDecimals(int v)
     updateText(d->quantity);
 }
 
-void QuantitySpinBox::setSchema(const Base::UnitSystem& s)
+void QuantitySpinBox::setSchema(const int s)
 {
     Q_D(QuantitySpinBox);
     d->scheme = Base::UnitsApi::createSchema(s);
@@ -732,7 +733,7 @@ QString QuantitySpinBox::getUserString(const Base::Quantity& val, double& factor
 {
     Q_D(const QuantitySpinBox);
     std::string unitStr;
-    std::string str = d->scheme ? val.getUserString(d->scheme.get(), factor, unitStr)
+    const std::string str = d->scheme ? val.getUserString(d->scheme.get(), factor, unitStr)
                                 : val.getUserString(factor, unitStr);
     unitString = QString::fromStdString(unitStr);
     return QString::fromStdString(str);