Add cache_size param with sqlite backend

Need a better way to deal with config, docker uses environment variables
mostly and the application uses .go files. Keeping the two in sync will
probably end up being annoying.

deploy/sqlite.env

@@ -1,2 +1,2 @@
-PANTSU_DBTYPE="sqlite3"
-PANTSU_DBPARAMS="./nyaa.db"
+PANTSU_DBTYPE=sqlite3
+PANTSU_DBPARAMS=./nyaa.db?cache_size=50