refactor: refactor migrations and add fixtures

feat: introduce key-value store
feat: imprint page (resolve #23)
chore: remove default user
chore: remove packr

migrations/common/fixtures/1_imprint_content.sql

@@ -0,0 +1,7 @@
+-- +migrate Up
+-- SQL in section 'Up' is executed when this migration is applied
+insert into key_string_values (`key`, `value`) values ('imprint', 'no content here');
+
+-- +migrate Down
+-- SQL section 'Down' is executed when this migration is rolled back
+delete from key_string_values where `key` = 'imprint';

migrations/sqlite3/2_key_value_table.sql

@@ -0,0 +1,11 @@
+-- +migrate Up
+-- SQL in section 'Up' is executed when this migration is applied
+create table key_string_values
+(
+    key      varchar(255) primary key,
+    value    text
+);
+
+-- +migrate Down
+-- SQL section 'Down' is executed when this migration is rolled back
+drop table key_string_value;