Disapprearred from addin menu when packages loaded

Prefixer options show up in addin menu if I start up a fresh R and only have base packages. Options disappeared once I loaded all my packages. However, If I set up the keyboard shortcuts, I can still call prefixer functions from the keyboard. Not sure if there is any conflict.

```
R version 4.0.0 (2020-04-24)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.3 LTS

Matrix products: default
BLAS: /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.7.1
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.7.1

locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8 LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=en_US.UTF-8
[8] LC_NAME=C LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] parallel stats4 stats graphics grDevices utils datasets methods base

other attached packages:
[1] rsvg_1.3 DOT_0.1 Rtsne_0.15 pheatmap_1.0.12 RColorBrewer_1.1-2 glmpca_0.1.0 ape_5.3
[8] edgeR_3.30.0 limma_3.44.1 DESeq2_1.28.0 SummarizedExperiment_1.18.0 DelayedArray_0.14.0 matrixStats_0.56.0 Biobase_2.48.0
[15] GenomicRanges_1.40.0 GenomeInfoDb_1.24.0 IRanges_2.22.1 S4Vectors_0.26.0 BiocGenerics_0.34.0 vroom_1.2.0 dplyr_0.8.5
[22] glue_1.4.0 assertthat_0.2.1 stringr_1.4.0 shinyjqui_0.3.3 shinytoastr_2.1.1 shinyAce_0.4.1 plotly_4.9.2.1
[29] ggplot2_3.3.0 networkD3_0.4 shinyTree_0.2.7 shinyWidgets_0.5.1 shinyjs_1.1 magrittr_1.5 rhandsontable_0.3.7
[36] pushbar_0.1.0 shinydashboardPlus_0.7.0 shinydashboard_0.7.1 shiny_1.4.0.9002

loaded via a namespace (and not attached):
[1] nlme_3.1-147 bitops_1.0-6 bit64_0.9-7 httr_1.4.1 tools_4.0.0 R6_2.4.1 DBI_1.1.0 lazyeval_0.2.2 colorspace_1.4-1
[10] withr_2.2.0 tidyselect_1.0.0 curl_4.3 bit_1.1-15.2 compiler_4.0.0 scales_1.1.0 genefilter_1.70.0 digest_0.6.25 XVector_0.28.0
[19] pkgconfig_2.0.3 htmltools_0.4.0.9003 prefixer_0.1.2.900 fastmap_1.0.1 htmlwidgets_1.5.1 rlang_0.4.5 rstudioapi_0.11 RSQLite_2.2.0 jsonlite_1.6.1
[28] BiocParallel_1.22.0 RCurl_1.98-1.2 GenomeInfoDbData_1.2.3 Matrix_1.2-18 Rcpp_1.0.4.6 munsell_0.5.0 lifecycle_0.2.0 yaml_2.2.1 stringi_1.4.6
[37] zlibbioc_1.34.0 grid_4.0.0 blob_1.2.1 promises_1.1.0 crayon_1.3.4 miniUI_0.1.1.1 lattice_0.20-41 splines_4.0.0 annotate_1.66.0
[46] locfit_1.5-9.4 pillar_1.4.3 igraph_1.2.5 markdown_1.1 geneplotter_1.66.0 XML_3.99-0.3 packrat_0.5.0 V8_3.0.2 data.table_1.12.8
[55] renv_0.9.3 vctrs_0.2.4 httpuv_1.5.2 gtable_0.3.0 purrr_0.3.4 tidyr_1.0.2 xfun_0.13 mime_0.9 xtable_1.8-4
[64] later_1.0.0 rsconnect_0.8.16 survival_3.1-12 viridisLite_0.3.0 tibble_3.0.1 AnnotationDbi_1.50.0 memoise_1.1.0 ellipsis_0.3.0
```

Reproduce the issue in R 4.0 on Ubuntu with a fresh session, then load the listed packages and compare the Prefixer addin menu with its keyboard shortcuts. Start by checking how the RStudio addin is exposed; done means the Prefixer options remain available after packages are loaded while keyboard invocation continues to work.

Written by the indexing model from the issue text.