Optimize loading time for "welspell_config"

[GegznaV]

When I try to open "welspell_config" window, on my PC it takes several seconds to open. Sometimes I start doubting if I even pressed the hot-key combination to open the tool.

I did some quick profiling. One of the bottlenecks on LanguageToolR side is function "lato_list_languages"

Next, lato_test_setup() is called several times.

Is it possible to optimize these processes?

Some ideas would be:

• to open window and load contents asynchronously: first, the window could be created and, next, the contents are updated. Some spinner of progress bar could be added to indicate, that the settings are still loading.
• to open the settings of spelling and grammar tools asynchronously (only when required tab is activated). It would be time saver especially if we need only one tool but not both.

[GegznaV]

One of the options would be to use stringi::stri_join() instead of paste() as stringi is already used as a dependency.

See awalker89/openxlsx#440 for details.

[nevrome]

What do you think about c3cfb3e? I wanted to do a PR, but my fingers where faster than my brain.

[GegznaV]

The result of Sys.setenv() is saved only for the current R session. For the repeated configuration in the same session, it helps, but for the first time configuration, it doesn't.

Note. If a method, which permanently saves the environment variable, is implemented, there should be a way to update the list of the languages if it changes. E.g., on the installation of the language tool. A new button could also be created for this purpose.