Bugfix/windows path

[murilopolese]

Problem:

File management and navigation on Windows wasn't working because of different path separators and root.
The previous solution of using cleanPath on the front end to normalize the path strings.
The path strings is calculated using four state properties:

• diskPath: The full path of the "working folder" on your disk
• diskNavigation: Tells the current folder you are, relative to diskPath
• serialPath: The serial port path
• serialNavigation: Tells the current folder you are, relative to `serialPath

Solution:

Instead of storing the serial port path on serialPath, that is now stored on serialPort.
serialPath is now always / since you can't choose a folder inside of your board to be the "working folder"

The function cleanPath was replaced by 3 different methods in the Serial and Disk objects declared on preload.js.

The 3 methods are:

• getFullPath(root, navigation, file): It's going to return the full resolved path
• getNavigationPath(navigation, target): Safely concatenate the target to current navigation
• getParentPath(filePath): Returns the parent path of a file or folder.

On Serial we can always assume UNIX-like filesystem so most of the methods will be basic string manipulation.
On Disk we use node's path module to comply to OS specification.

All ipcMain methods expect now a fully resolved file/folder path.

Extra:

Improve speed of downloading files without unsaved changes by simply saving the current editor content on disk.

[ubidefeo]

Tested the improvements in Windows VM and it works.
No regressions introduced to Mac

[ubidefeo]

fixes #50

[kittaakos]

Thanks for the fixes on Windows. Please go ahead with the merge, and let's revisit the path handling later.