implemented server database and api for client database

src/server/db/server_db_internal.h

@@ -0,0 +1,27 @@
+#pragma once
+#include "server_db.h"
+
+typedef struct ServerQueries {
+    struct {
+        /* (id, name, description) -> void */
+        tsqlite_statement* insert;
+        /* (id, name, description) -> void */
+        tsqlite_statement* update;
+        /* (id) -> 1 or nothing */
+        tsqlite_statement* exists;
+    } channels;
+    struct {
+        /* (channel_id, sender_id, content) -> (id, timestamp) */
+        tsqlite_statement* insert; 
+        /* (channel_id, first_message_id, count) -> [(id, sender_id, content, timestamp)] */
+        tsqlite_statement* get_block;
+    } messages;
+    struct {
+        /* (username, token) -> (id, registration_time) */
+        tsqlite_statement* insert;
+        /* (username) -> (id) */
+        tsqlite_statement* find_by_username;
+        /* (id, token) -> 1 or nothing */
+        tsqlite_statement* compare_token;
+    } users;
+} ServerQueries;