common/param_package: Implement lists and nested data structures.

Implements the handling of arbitrarily complex data structures.
The following are supported:
- Lists (like `key:[val1|val2|...]`)
- Dictionaries/Maps (like `key:[k1:v1,k2:[v2a,v2b]]`)

Lists of Dictionaries/Maps look a bit different:
```
key:[k1:v1,k2:[v2a,v2b]|a:x,b:y]
     \_______________/  \_____/
           dict1         dict2
```

src/common/param_package.h

@@ -7,6 +7,7 @@
 #include <initializer_list>
 #include <map>
 #include <string>
+#include <vector>
 
 namespace Common {
 
@@ -25,12 +26,30 @@ public:
     ParamPackage& operator=(ParamPackage&& other) = default;
 
     std::string Serialize() const;
+
+    // Getters
     std::string Get(const std::string& key, const std::string& default_value) const;
+    std::vector<std::string> Get(const std::string& key,
+                                 const std::vector<std::string>& default_value) const;
     int Get(const std::string& key, int default_value) const;
+    std::vector<int> Get(const std::string& key, const std::vector<int>& default_value) const;
     float Get(const std::string& key, float default_value) const;
+    std::vector<float> Get(const std::string& key, const std::vector<float>& default_value) const;
+    ParamPackage Get(const std::string& key, const ParamPackage& default_value) const;
+    std::vector<ParamPackage> Get(const std::string& key,
+                                  const std::vector<ParamPackage>& default_value) const;
+
+    // Setters
     void Set(const std::string& key, std::string value);
+    void Set(const std::string& key, std::vector<std::string> value);
     void Set(const std::string& key, int value);
+    void Set(const std::string& key, std::vector<int> value);
     void Set(const std::string& key, float value);
+    void Set(const std::string& key, std::vector<float> value);
+    void Set(const std::string& key, ParamPackage value);
+    void Set(const std::string& key, std::vector<ParamPackage> value);
+
+    // Other methods
     bool Has(const std::string& key) const;
     void Erase(const std::string& key);
     void Clear();
@@ -43,6 +62,24 @@ public:
 
 private:
     DataType data;
+
+    /**
+     * Replace complex data structures with placeholders, and generate the lookup table.
+     * The lookup table is emptied before being used.
+     */
+    static std::string PlaceholderifyData(const std::string& str, std::vector<std::string>& lookup);
+
+    /**
+     * Replace placeholders (in-place) with original data obtained from a lookup table.
+     */
+    static void ReplacePlaceholders(std::string& str, const std::vector<std::string>& lookup);
+
+    /**
+     * Replace placeholders with original data obtained from a lookup table and returns the
+     * resultant string.
+     */
+    static std::string ReplacePlaceholders(const std::string& str,
+                                           const std::vector<std::string>& lookup);
 };
 
 } // namespace Common