Add Shop interface

src/main/java/com/alttd/playershops/api/Shop.java

@@ -0,0 +1,44 @@
+package com.alttd.playershops.api;
+
+import com.alttd.playershops.shop.ShopType;
+import org.bukkit.Location;
+import org.bukkit.inventory.ItemStack;
+
+import java.util.UUID;
+
+public interface Shop { // TODO finish docs
+
+    String getOwnerName();
+
+    UUID getOwnerUUID();
+
+    ShopType getType();
+
+    Location getSignLocation();
+
+    Location getContainerLocation();
+
+    String getServer();
+
+    double getPrice();
+
+    void setPrice(double price);
+
+    int getAmount();
+
+    void setAmount(int amount);
+
+    double getBalance();
+
+    void setBalance(double balance);
+
+    ItemStack getItemStack();
+
+    void setItemStack(ItemStack itemStack);
+
+    ItemStack getSecondaryItem();
+
+    void setSecondaryItem(ItemStack itemStack);
+
+    boolean isInitialized();
+}