Refactor the internal sql interface somewhat

Experiment with refactoring the internal sql interface a bit.  My
original goal was to modify the schema and thus refactor to a state
where it would be sane to write tests for dc_sqlite_open() (and/or
however it ends up refactored) to assert schame changes before/after.

src/dc_loginparam.rs

@@ -62,7 +62,7 @@ pub unsafe fn dc_loginparam_empty(mut loginparam: *mut dc_loginparam_t) {
 pub unsafe fn dc_loginparam_read(
     context: &Context,
     loginparam: *mut dc_loginparam_t,
-    sql: &dc_sqlite3_t,
+    sql: &SQLite,
     prefix: *const libc::c_char,
 ) {
     let mut key: *mut libc::c_char = 0 as *mut libc::c_char;
@@ -143,7 +143,7 @@ pub unsafe fn dc_loginparam_read(
 pub unsafe fn dc_loginparam_write(
     context: &Context,
     loginparam: *const dc_loginparam_t,
-    sql: &dc_sqlite3_t,
+    sql: &SQLite,
     prefix: *const libc::c_char,
 ) {
     let mut key: *mut libc::c_char = 0 as *mut libc::c_char;