Refactor constructors of some classes

Classes like `ButtonEditDialog` `JoyButtonSlot` (and probably many other) have many duplications in overrides constructors.

For example

```cpp
JoyButtonSlot::JoyButtonSlot(QObject *parent)
: QObject(parent)
, extraData()
{
deviceCode = 0;
m_mode = JoyKeyboard;
m_distance = 0.0;
previousDistance = 0.0;
qkeyaliasCode = 0;
easingActive = false;
mix_slots = nullptr;
}

JoyButtonSlot::JoyButtonSlot(int code, JoySlotInputAction mode, QObject *parent)
: QObject(parent)
, extraData()
{
deviceCode = 0;
qkeyaliasCode = 0;

if (code > 0)
deviceCode = code;

m_mode = mode;
m_distance = 0.0;
easingActive = false;
mix_slots = nullptr;
}

JoyButtonSlot::JoyButtonSlot(int code, int alias, JoySlotInputAction mode, QObject *parent)
: QObject(parent)
, extraData()
{
deviceCode = 0;
qkeyaliasCode = 0;

if (code > 0)
deviceCode = code;

if (alias > 0)
qkeyaliasCode = alias;

m_mode = mode;
m_distance = 0.0;
easingActive = false;
mix_slots = nullptr;
}
```
Instead of duplicating code, these constructors could call each other