Fix external folder manipulation (fix #232)

[Enfyve]

Updates folder upon navigation (up, back, forward, in).

Also introduces a new button to refresh the current folder view when pressed or when hotkey pressed (F5 or Ctrl+R)

Scenarios tested:

• navigate in
• navigate up
• navigate forward
• navigate backward
• click refresh button
• press F5
• press Ctrl+R
• change file type
• change view

[dacap]

Hi @Enfyve, from what I can see from the PR it will invalidate cached items in all actions, does removing this condition achieve the same effect?

[Enfyve]

@dacap removing the condition alone does not, however further adjusting the condition does achieve the same effect in most scenarios except when adjusting views

+++  if (isFolder() ||
---  if (isFolder() &&
      // if the children list is empty, or the file-system version
      // change (it's like to say: the current m_children list
      // is outdated)...
+++      !m_children.empty()) {
---      (m_children.empty() ||
---       current_file_system_version > m_version)) {

[dacap]

Finally merged with several changes/fixes:

• f41c6bc
• debd220
• db84c02
• 9248f53
• c782741

Mainly the list of files is not refreshed each time we change between folders (so the cache is not invalidated). Anyway a pending change to finally fix #232 would be something like #3275

[dacap]

And finally I almost forgot, thanks @Enfyve for this patch and the patience.