Support pylama for python (#2266)

* Add pylama for python
* Consolidate python traceback handling

ale_linters/python/flake8.vim

@@ -74,15 +74,11 @@ let s:end_col_pattern_map = {
 \}
 
 function! ale_linters#python#flake8#Handle(buffer, lines) abort
-    for l:line in a:lines[:10]
-        if match(l:line, '^Traceback') >= 0
-            return [{
-            \   'lnum': 1,
-            \   'text': 'An exception was thrown. See :ALEDetail',
-            \   'detail': join(a:lines, "\n"),
-            \}]
-        endif
-    endfor
+    let l:output = ale#python#HandleTraceback(a:lines, 10)
+
+    if !empty(l:output)
+        return l:output
+    endif
 
     " Matches patterns line the following:
     "
@@ -90,7 +86,6 @@ function! ale_linters#python#flake8#Handle(buffer, lines) abort
     "
     " stdin:6:6: E111 indentation is not a multiple of four
     let l:pattern = '\v^[a-zA-Z]?:?[^:]+:(\d+):?(\d+)?: ([[:alnum:]]+):? (.*)$'
-    let l:output = []
 
     for l:match in ale#util#GetMatches(a:lines, l:pattern)
         let l:code = l:match[3]