Dedicated declation module

[Zomtir]

Replace the datadeclaration and datadisclaimer by a struct with more info.

Current iteration

pub struct Declaration {
    pub declaration_id: u8,
    pub title: String,
    pub url: Option<String>,
    pub disclaimer: Option<String>,
    pub signed: Option<chrono::NaiveDate>,
    pub terminated: Option<chrono::NaiveDate>,
}