migrations: dsl for describing them; applying it to virtual db schema to check correctness; storing final schema to file

--HG--
rename : tpl/internal/ocaml_type_gen_post.ml => tpl/internal/common/ocaml_type_gen_post.ml
rename : tpl/internal/ocaml_type_gen_pre.ml => tpl/internal/common/ocaml_type_gen_pre.ml
rename : tpl/internal/proj_common.ml => tpl/internal/common/proj_common.ml
rename : tpl/internal/views_pre.ml => tpl/internal/common/views_pre.ml
rename : tpl/internal/command_db_create.ml => tpl/internal/server/command_db_create.ml
rename : tpl/internal/command_db_drop.ml => tpl/internal/server/command_db_drop.ml
rename : tpl/internal/database.ml => tpl/internal/server/database.ml
rename : tpl/internal/main_post.ml => tpl/internal/server/main_post.ml
rename : tpl/internal/main_pre.ml => tpl/internal/server/main_pre.ml
rename : tpl/internal/psql.ml => tpl/internal/server/psql.ml
rename : tpl/internal/viewHelpers.ml => tpl/internal/server/viewHelpers.ml