commands/thread: Add option --strip_ansi to pipeto

If someone has a mailcap entry that colors the mail content, it is
possible that she would want to get the content without the CSI escapes
when piping it an external command.

Ideally, there should be a way to have the content untouched by the
mailcap filter so we could use it when it makes sense. However, let's
use ansi.remove_csi() for the time being.

alot/commands/thread.py

@@ -645,6 +645,8 @@ def apply(self, ui):
                    'help': 'let the shell interpret the command'}),
     (['--notify_stdout'], {'action': 'store_true',
                            'help': 'display cmd\'s stdout as notification'}),
+    (['--strip_ansi'], {'action': 'store_true',
+                       'help': 'remove ANSI CSI escapes from the content'}),
 ])
 class PipeCommand(Command):
 
@@ -653,7 +655,7 @@ class PipeCommand(Command):
 
     def __init__(self, cmd, all=False, separately=False, background=False,
                  shell=False, notify_stdout=False, format='raw',
-                 add_tags=False, noop_msg='no command specified',
+                 add_tags=False, strip_ansi=False, noop_msg='no command specified',
                  confirm_msg='', done_msg=None, **kwargs):
         """
         :param cmd: shellcommand to open
@@ -676,6 +678,8 @@ def __init__(self, cmd, all=False, separately=False, background=False,
         :type format: str
         :param add_tags: add 'Tags' header to the message
         :type add_tags: bool
+        :param strip_ansi: remove ANSI CSI escapes from the content
+        :type strip_ansi: bool
         :param noop_msg: error notification to show if `cmd` is empty
         :type noop_msg: str
         :param confirm_msg: confirmation question to ask (continues directly if
@@ -695,6 +699,7 @@ def __init__(self, cmd, all=False, separately=False, background=False,
         self.notify_stdout = notify_stdout
         self.output_format = format
         self.add_tags = add_tags
+        self.strip_ansi = strip_ansi
         self.noop_msg = noop_msg
         self.confirm_msg = confirm_msg
         self.done_msg = done_msg
@@ -745,6 +750,9 @@ async def apply(self, ui):
                     msgtext = '%s\n\n%s' % (headertext, bodytext)
                     pipestrings.append(msgtext)
 
+        if self.strip_ansi:
+            pipestrings = [ansi.remove_csi(s) for s in pipestrings]
+
         if not self.separately:
             pipestrings = [separator.join(pipestrings)]
         if self.shell: