make tasks.sh search for local .tasks

[franciscolourenco]

storing all your tasks files in one folder in dropbox is one approach.

given one wants to sync the tasks of a project, one will also probably want to sync the project folder itself,
another approach would be to store each task file in the respective project's folder, and then use whatever (dropbox, git, hg, svn) to sync the folder.

tasks.sh should first check for the existence of any .tasks files in the current folder, and only then default to the dropbox folder.
in addition, it should accept a path for a specific .tasks file

[pkamenarsky]

82e7bb3

tasks.sh now looks for the first .tasks file in the local dir and switches to the Dropbox location only if there's none.

The specific .tasks file argument is gonna need more work since the script will now need to parse the -o and -f flags in arbitrary order etc - and since I'm a bash script noob I'm gonna leave this for a pull request :)