There is no File Type for Tables.
You can only define extensions for:
- function
- procedure
- trigger
- package spec
- package body
- package
- type spec
- type body
- type
- java source
- others (it does not work for tables or sequences)
and
- project files
- sql scripts
- report files
- test scripts
- command files
- diagramm files
so there is no option for sequences or tables to define the extension.