[Bug]: Buckets generated by `draggable_buckets` are not bookmarkable

JS in `draggable_buckets` precludes `shiny`-bookmarking of `arm_ref_comp_observer`.

See for example this module:

```
library(nestcolor)
library(dplyr)

ADSL <- tmc_ex_adsl
ADRS <- tmc_ex_adrs %>%
mutate(AVALC = d_onco_rsp_label(AVALC) %>%
with_label("Character Result/Finding")) %>%
filter(PARAMCD != "OVRINV" | AVISIT == "FOLLOW UP")

arm_ref_comp <- list(
ARM = list(
ref = "B: Placebo",
comp = c("A: Drug X", "C: Combination")
),
ARMCD = list(
ref = "ARM B",
comp = c("ARM A", "ARM C")
)
)

app <- init(
data = cdisc_data(
ADSL = ADSL,
ADRS = ADRS,
code = "
ADSL <- tmc_ex_adsl
ADRS <- tmc_ex_adrs %>%
mutate(AVALC = d_onco_rsp_label(AVALC) %>%
with_label(\"Character Result/Finding\")) %>%
filter(PARAMCD != \"OVRINV\" | AVISIT == \"FOLLOW UP\")
"
),
modules = modules(
tm_g_forest_rsp(
label = "Forest Response",
dataname = "ADRS",
arm_var = choices_selected(
variable_choices(ADSL, c("ARM", "ARMCD")),
"ARMCD"
),
arm_ref_comp = arm_ref_comp,
paramcd = choices_selected(
value_choices(ADRS, "PARAMCD", "PARAM"),
"INVET"
),
subgroup_var = choices_selected(
variable_choices(ADSL, names(ADSL)),
c("BMRKR2", "SEX")
),
strata_var = choices_selected(
variable_choices(ADSL, c("STRATA1", "STRATA2")),
"STRATA2"
),
plot_height = c(600L, 200L, 2000L),
default_responses = list(
BESRSPI = list(
rsp = c("Stable Disease (SD)", "Not Evaluable (NE)"),
levels = c(
"Complete Response (CR)", "Partial Response (PR)", "Stable Disease (SD)",
"Progressive Disease (PD)", "Not Evaluable (NE)"
)
),
INVET = list(
rsp = c("Complete Response (CR)", "Partial Response (PR)"),
levels = c(
"Complete Response (CR)", "Not Evaluable (NE)", "Partial Response (PR)",
"Progressive Disease (PD)", "Stable Disease (SD)"
)
),
OVRINV = list(
rsp = c("Progressive Disease (PD)", "Stable Disease (SD)"),
levels = c("Progressive Disease (PD)", "Stable Disease (SD)", "Not Evaluable (NE)")
)
)
)
)
)

runApp(app, launch.browser = TRUE)
```