replace bower for sao

the website for bower, used in the build of SAO, has recommended using alternatives since 2017, and development has halted since. to future-proof the build, it would seem preferable to perhaps switch to alternatives.

(for context, my use-case is packaging Tryton SAO for Nix, which bower complicates.)

if it helps, i am willing to submit a pull request for this (if i know what build system might be preferred).