Refactor battlers to make it easier to edit and extend them

Also improved combat actions and moved some calculations out of battlers and into the actions instead.

closes #101

Leader and followers created from party in LocalMap

Characters dialogue database and portraits added

Fixed CoC link in README

I opted to serve the textures with a function in the database that handles the fetching of the desired texture. It looked more natural, easier and more natural than to add this logic to the Dialogue.gd since all it does is returning the Dictionary with the dialogue phrases, the actual building of the interface happens in DialogueBox. There, I fetch the textures by reaching to the database. 

Closes #92

Closes #90

After the filename of the CoC changed, the README was not updated.

Fix #88 - missing skills now decrease mana properly

I tried to simplify the code, shorten the player script
The DialogueBox now uses the pressed signal on buttons for better mouse and touch support in the future

closes #80

Update the changelog for v0.2.0

Add version number to the project

Remove Munro

I temporarily changed the colors, but the label will need more work. Maybe a bitmap font instead of actual text: there are some artifacts with scale animation

Make default.theme's panel background transparent
The panel now takes the width of the screen and anchors to the top of the window
closes #78

Refactor CircularButton to extend Button
Disable if Battler.can_use_skill is false
Closes #77