Support for Devanagari (Contd...)

With new findings, I want to raise issue #703 again.

The problem with conjuncts is that if I set the info for the conjuncts glyphs (Edit > Info for Selection):
☑️ Script: "devanagari"
☑️ Category: "Letter"
☑️ Subcategory: "Other"

then GlyphsApp does not include those in the `cjct (Conjunct Forms)` feature, thus not substituting those correctly with `cjct_devanagari` in the generated font (eg. `sub tt-deva ya-deva by tt_ya-deva;` gets missing).

If I set the glyph info in the way mentioned above and on the issue #703, then Glyph does not correctly add those to `cjct_devanagari` and here's how `fontmake` generated font looks for "ट्यूब":

And, if I uncheck `Subcategory` from the glyph info (or set it to "Ligature"), then, here's how `fontmake` generated font looks for "ट्यूब":

Thank you. Plz let me know how can I help.