hosts: new widget for Hosts table (#1465)

The `SatTable` widget is modified to ignore hidden headers and columns in the table.
Hidden duplicate columns cause the widget to work incorrectly internally,
while on the outside everything seems in order.

This behavior is especially present in the Hosts table,
where instead of seemingly interacting with the visible columns,
the widget interacts with the hidden ones.

The table widget for Hosts somehow worked properly(-ish),
until commit 886a1a8 exposed this flaw.

Excluding the hidden columns during the table cells collection
by the widget solves the problem.

airgun/widgets.py

@@ -1881,6 +1881,8 @@ class SatTable(Table):
  If the table is empty, there might be only one column with an appropriate message in the table
  body, or it may have no columns or rows at all. This subclass handles both possibilities.
 
+ It also ignores all hidden columns, which some tables might contain, like the Hosts table.
+
  Example html representation::
 
  <table bst-table="table" ...>
@@ -1907,6 +1909,10 @@ class SatTable(Table):
 
  """
 
+ HEADERS = "./thead/tr/th[not(@hidden)]|./tr/th[not(@hidden)]|./thead/tr/td[not(@hidden)]"
+ COLUMN_RESOLVER_PATH = "/td[not(@hidden)]"
+ COLUMN_AT_POSITION = "./td[not(@hidden)][{0}]"
+
  no_rows_message = (
  ".//td/span[contains(@data-block, 'no-rows-message') or "
  "contains(@data-block, 'no-search-results-message')]"