Adjust the size of the elements in the statusbar

Use the same height for all the elements and try to prevent
variations of the speed labels.
Show current speed limits in the status bar

Closes #1316.
Implement episode filter for rss downloader
Add tooltip to episode filter text edit
Fix missing icon for open action in file list
Fix configure script when running with dash

`test 1 == 1` will fail using dash as the default shell. The `test 1 = 1`
syntax works in both Bash and Dash.
Merge pull request #2156 from jleclanche/master

Fix configure script when running with dash
Reduce the number of torrent_handle::torrent_file() calls in QTorrentHandle::prioritize_files(). Closes #2161.

It was reported (#2161) that enabling/disabling a downloading of a file
is considerably slow on libtorrent 1.0.3, but not on 0.16.x. The problem
is that a function torrent_file() in libttorrent 1.0.3 does a deep copy
of torrent_info, while get_torrent_info() in libtorrent 0.16.x only
returns a reference.
Merge pull request #2163 from sorokin/optimize-prioritize-files

Reduce the number of torrent_handle::torrent_file() calls in QTorrentHandle::prioritize_files()
Merge pull request #800 from Gelmir/smart_ep

Implement episode filter for rss downloader
Set placeholder text to torrent content filter.

In commit afb03725ad8fcf6eb1db305bdc89391a573f5968 it was implemented
for torrent list filter. Now it is here for files filter.
Documenting the project's coding guidelines. Closes #2091.
Set piece size to (max) 4Mb instead of empty string when created torrent
is very large.
Fix emptying of piece size combobox when user checks "auto" checkbox.

The function computePathSize returns -1 if file isn't found, not 0.
Merge pull request #2173 from sorokin/placeholder-text-torrent-list

Set placeholder text to torrent content filter.
Merge pull request #2174 from sorokin/fix-empty-combobox

Fix emptying of 'piece size' combobox when user enable 'auto' checkbox and no files are selected
Implement open & select file in file manager [Windows only]
Fix opening of samba shares
Merge pull request #744 from Gelmir/open_select

[Windows] Implement open & select file in file manager
Escape backslashes. Issue #800.