treewide: use StaticFiles() rather than rel path

This commit is not exhaustive, and it is a trend in this codebase to not
use StaticFiles() and instead use relative paths. This means the code
cannot run anywhere other than the source code directory, as it will not
find the files it is looking for

lnbits/extensions/splitpayments/__init__.py

@@ -12,7 +12,7 @@ db = Database("ext_splitpayments")
 splitpayments_static_files = [
     {
         "path": "/splitpayments/static",
-        "app": StaticFiles(directory="lnbits/extensions/splitpayments/static"),
+        "app": StaticFiles(packages=[("lnbits", "extensions/splitpayments/static")]),
         "name": "splitpayments_static",
     }
 ]
@@ -22,7 +22,7 @@ splitpayments_ext: APIRouter = APIRouter(
 
 
 def splitpayments_renderer():
-    return template_renderer(["lnbits/extensions/splitpayments/templates"])
+    return template_renderer([StaticFiles(packages=[("lnbits", "extensions/splitpayments/static/templates")])])
 
 
 from .tasks import wait_for_paid_invoices